Title:
Current Status of Composition and Somatic Cell Count in Milk of Goats Enrolled in Dairy Herd Improvement Program in the United States S.S. ZENG1,*, L. ZHANG1,2, G.R. WIGGANS3, J. CLAY4, R. LACROIX5, J.Z. WANG1, and T. GIPSON1 1
E (Kika) de la Garza American Institute for Goat Research, Langston University, Langston, OK 73050, USA; 2
Northeast Agricultural Research Center of China, Changchun, Jilin 130124, China; 3
Animal Improvement Programs Laboratory, USDA-ARS, Beltsville, MD 20705, USA; 4
Dairy Records Management Systems, North Carolina State University, Raleigh, NC 27603, USA; 5
Key words:
AgSource Cooperative Services, Verona, WI 53593, USA.
Formatted: Line spacing: single
Goat milk, DHI, somatic cell count, milk production
* To whom correspondence to be addressed. S. Steve Zeng, Ph.D. P.O. Box 1730 Langston University Langston, Oklahoma 73050, USA Phone: (405)466-6103 Fax: (405)466-6180 E-mail:
[email protected]
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ABSTRACT The effects of breed, parity, stage of lactation (month), herd size, and regions/states on fat and protein content, somatic cell count (SCC) and production of milk from dairy goats enrolled in the Dairy Herd Improvement (DHI) program in the United States (U.S.) in 2007 were investigated to monitor the current status of composition and SCC and to help goat producers improve their herd management and receive premiums for high quality goat milk. Statistical analysis of composite DHI data indicated that composition, SCC and production of goat milk were affected by many non-infectious factors. Marked variations (P < 0.05) in fat and protein content and milk production were found among goat breeds, particularly among those non-registered goats. In the first five parities, milk fat and protein content was relatively constant, however, a sharp decline (P < 0.05) was observed in parity 6. As parities increased, SCC in milk increased steadily (P < 0.05). Significant differences (P < 0.05) in all variables were discovered among regions. Large herds of goats tended to have lower milk fat and protein content but higher milk production and SCC than the small herds (P < 0.05). The above findings suggest that it be economically imperative to consider culling goats after their fifth lactation and that year-round breeding and lactation programs be practiced, if dairy goat producers in the U.S. are to meet the Grade “A” goat milk requirements. All factors that contributed to variations in fat, protein, SCC and production of goat milk should be taken into consideration when establishing price incentive systems for goat milk.
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INTRODUCTION Dairy goat farming has long been a tradition worldwide and is a vital sector of national economy in many developed countries in the Mediterranean region as well as in many developing countries such as India and China. Dairy cows contribute the greatest amount of milk for human consumption in today’s cow-oriented society; however, dairy goats provide much-needed nutrition to a larger proportion of the population in the whole world who do not have the access to cow milk and an alternative to cow milk for those who are allergic to cow milk [1]. While home consumption of goat milk today is still mainly for the prevention of under-nutrition and malnutrition, as goat milk is a premium source of calcium and protein to people in many countries where cow milk is not available or not affordable, an increasing amount of goat milk is processed into dairy products such as cheeses, pasteurized liquid milk, powdered milk, yogurt, ice cream, smoothie, etc. in commercial processing facilities or on the farm in both developing and developed countries [2]. According to FAOSTAT [3], the number of dairy goats in the world reached more than 160 million in 2006, while goat milk production surpassed 13.8 million metric tones, representing significant increases of 12 and 15%, respectively, as compared to a decade ago. Top twenty countries with the highest dairy goat inventories are displayed in Table 1. Of these leading countries, almost all of them are under-developed. Overall, 93.5% of dairy goats in the world are distributed in the developing countries. Therefore, dairy goat farming is not only an important agricultural segment of national economy especially in India, Sudan, Bangladesh and Iran, but also an imperative source of food for a vast population in the whole world. In the United States (U.S.), the dairy goat industry has started to play a viable role in enhancing the household income of goat producers and making small-scale dairy farms sustainable. Over the last 25 years, goat milk and dairy products have been recognized and accepted by many Americans, particularly by some ethnic groups and health conscious consumers, as unique specialty food products. According to the most recent Agriculture Census of 2002 (http://www.agcensus.usda.gov/Publications/2002/), the dairy goat inventory in the U.S. had more than doubled in the previous decade (from 125,000 head in 1992 to197,000 in 2002). The agricultural statistics released by the National Agricultural Statistics Service (NASS) of United States Department of Agriculture (USDA) in February 2008 (Sheep and Goats, Mt An 5-2) shows that the number of dairy goats has risen to 305,000 in 2007, indicating an astounding increase of 55% in the last five years. Among the top 20 dairy goat producers, Wisconsin, California, and Texas are the leading states with at least 23,000 lactating dairy goats (Table 2). Goat milk sales in the U.S. are mainly for fluid milk consumption and dairy processing, such as cheeses and powdered milk. The functional properties and the unique characteristics of goat milk seem to have positively impacted the demand of consumers for goat milk and cheeses not only in the U.S. but also throughout the world. Because of the increasing trend of dairy goats in the U.S. and the systematic research in goat milk and dairy products around the world since early 1980s, the American Institute for Goat Research at Langston University, Oklahoma, established in the mid 1990s a certified Dairy Herd Improvement (DHI) laboratory specifically for dairy goats in the U.S. This commercial laboratory has analyzed composition and SCC of goat milk sample processed data, generated monthly/yearly reports, and provided service to dairy goat producers from all over the U.S. In addition, it provides an excellent tool for research and extension activities to help promote the dairy goat industry. As specified in the Pasteurized Milk Ordinance (PMO) [4] , Grade “A” goat milk must not exceed 1.0×106/ml in somatic cell count (SCC). It is generally agreed that SCC in goat milk is typically high compared to that in cow milk and is a less useful indication of 3
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udder health [5]. Somatic cell count in goat milk has been a major issue for the last two decades as it is commonly regarded as an indicator of milk quality. Paape et al. [6] monitored goat milk SCC during a five year span (2000-2004) using USDA data and reported an increasing trend of SCC in recent years. They also noticed a large variation among dairy goat breeds, with Toggenburg having the greatest and Oberhasli having the least variation. In addition, SCC in goat milk increased as lactation and parity advanced. Because of various climates, state/area was reported to contribute to the SCC variation as well. Besides udder health, research has identified many other factors affecting SCC in goat milk, such as breed, parity, stage of lactation, milking procedure, morning or evening milking, sample shipping, testing methods (automated machine counting vs. pyronin-Y methyl green direct microscopic counting), testing laboratory, milking methods (hand or machine milking) [7-11]. In addition, Zeng [12] stated that it is imperative to use goat milk SCC standards for monthly calibration for more accurate assessment of SCC in goat milk if an automated counter is used [12]. Paape and co-workers [6] reported that non-infectious factors such as parity and stage of lactation had a major impact on SCC and further suggested that all factors be considered when establishing new SCC legal limits for goat milk [6]. Because of extensive and scientific evidences, the National Conference on Interstate Milk Shipment (NCIMS) in the U.S. has established a separate SCC limit of one million per milliliter for Grade “A” goat milk, whereas Grade “A” cow milk is presently 750,000/ml. The SCC limit for goat milk will continue to be unchanged while the cow milk counterpart is being considered to be further lowered to 400,000/ml. However, no reports have been found on fat and protein contents in goat milk. In European countries such as France, Spain, and Norway, quality incentive payment systems take into consideration fat and protein content, SCC, and bacterial counts [13], although there is currently no legal limit for SCC in the European Union [6]. A payment system in relation to goat milk quality has also been implemented and has helped advance the dairy goat industry in other countries and regions such as Italy, the Netherlands, and Taiwan. Most dairy goats in the U.S. are seasonal, kidding in March and drying off in November or December. Dairy goat herds in North America are small scale, scattered around and distant from processing facilities. Currently, there are no standard mechanisms in the U.S. to establish incentive payment systems for goat milk. One attempt has been reported by Haenlein [14] to implement a quality payment system for goat milk using cow dairies as a model for goat dairies on a regional scale or by individual dairy processors, because of insufficient data available for dairy goats [14]. The analysis and interpretation of Dairy Herd Improvement (DHI) data (i.e., fat, protein and SCC) with a large number of dairy goats and on a broad base of regions/states during an entire year 2007 should help establish a scientific foundation and fill the void. Therefore, the objective of this study was to investigate the effects of breed, parity (i.e., lactation number), stage of lactation (month), herd size, and regions/states on the distribution of milk fat and protein contents, SCC and milk production of dairy goats enrolled in the DHI program throughout a year to help goat producers improve their herd management, receive premiums for high quality goat milk, and improve the sustainability of dairy goat farming in the U.S. MATERIALS AND METHODS
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General description of dairy goats and DHI data. DHI data of dairy goats for this study were generated in three DHI laboratories/centers, i.e., Langston University DHI Laboratory for Goats in OK, Dairy Records Management Systems in Raleigh, NC, and AgSource Cooperative Services in Verona, WI and provided by the Animal Improvement Programs Laboratory (AIPL) of USDA. A total of 29,045 test samples from 6,026 lactating does were included in this study, covering a wide range of states/regions (38 states in all) in 4
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the U.S. for the entire year 2007. Of the registered or recorded dairy breeds of American Dairy Goat Association (ADGA), Alpine (AI, n = 1,939), Nubian (NU, n = 936), Sannen (EN, n = 831), La Mancha (LN, n = 575), Toggenburg (TO, n = 384), and Oberhasli (OH, n = 291), accounted for 86% of all dairy goats. The other breeds, Experimental (EX), Sable (CC), Mixed (XX), Nigerian Dwarf (ND), and Pygmy (PY), were also included as their popularity has increased in the U.S. in the last decade.
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Analyses of composition and SCC. Goat milk samples were collected monthly from individual herds enrolled in the DHI program in 2007. The samples were composite of evening and morning milkings and preserved with Microtabs (D&F Control Systems, Inc., Dublin, CA, USA). These samples were shipped in a milk shipping box to DHI laboratories and analyzed for composition (fat and protein) and SCC. All the DHI laboratories used Foss instruments (Foss North America, Eden Prairie, MN, USA) and/or Bentley machines (Bentley Instruments Inc., Chaska, MN, USA). All instruments were calibrated monthly and certified by Quality Certification Service as authorized by the National Dairy Herd Improvement Association.
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Statistical analysis. Dairy goat data from three DHI laboratories/centers were analyzed using the general linear model (GLM) mixed models (Proc Mixed) of SAS [15]. Dependent variables were fat, protein, SCC and production of milk (kg/d per doe). Actual SCC data were log transformed for statistical analysis and then back-transformed for data interpretation and result discussion. If there were significant effects of breed, parity, stage of lactation (month), herd size, region, and interactions among them, mean comparisons were performed using least significant differences (LSD). RESULTS AND DISCUSSION Overall means of fat %, protein %, actual SCC (×105/ml), and production (kg/d per doe) of milk are presented in Table 3. As indicated in the PMO [4], Grade “A” goat milk sold in retail packages must contain >2.5% fat and >7.5% solids not fat, and the Grade “A” goat milk must not exceed the SCC limit of 1.0×106/ml. The overall SCC of 3.92×105/ml in milk from all goats tested, along with 3.81% fat and 3.15% protein, would meet the Grade “A” requirements for goat milk rather easily. The real challenge is what portion of the herds would fail to meet the requirement. Therefore, a cumulative distribution function plot of SCC is presented in Figure 1. Twenty-four percent of goat milk samples tested in 2007 exceeded the current 1.0×106/ml limit. As much as 31% would have failed the current SCC limit of 7.5×105/ml for cow milk. Only 50% of the goat milk samples would meet the cow milk limit of 4.0×105/ml being proposed in the U.S. Recently, Miller et al. (2008) examined SCC of cow milk from DHI herds in the U.S. during 2007 [16]. They reported that only 3.5 and 24% of the test day cow milk samples had exceeded the current and the proposed limits, respectively. Therefore, the findings in this study suggest that the current SCC limit of 1.0×106/ml for Grade “A” goat milk be retained, while its counterpart for Grade “A” cow milk is to be further lowered to 4.0×105/ml. Any attempt to apply a cow milk SCC limit to goat milk will prove to be unjustified. Effect of breed on fat, protein, SCC and production. As shown in Figure 2 (a, b, e and f), breed of dairy goats had marked influence (P < 0.05) on fat and protein contents, milk production, and SCC. Milk of Nigerian Dwarf (ND) goats had the highest fat percentage (6.39%), which was more than double than that of Sable (CC) milk (3.04%). Among the six major dairy breeds, milk of Nubian (NU) was the highest in fat content while that of Toggenburg (TO) was the lowest (P < 0.05). Nigerian Dwarf (ND) and Pygmy (PY) milk showed the highest protein percentage (4.37 and 4.35%, respectively) among all breeds (P < 0.05). Milk of Sable (CC) and Toggenburg (TO) had the lowest fat and protein percentage (P 5
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< 0.05) in comparison with that of other breeds. However, Sable (CC) goats had the highest milk production (3.88 kg/d per doe) (P < 0.05), while Pygmy (PY) and Nigerian Dwarf (ND) goats were the lowest. It must be noted though that only 111 Sable (CC) milk samples from 27 lactating does were collected in the whole year. Significant differences (P < 0.05) in milk production were observed among the six major dairy breeds in a decreasing order of Alpine (AI), Sannen (EN), Oberhasli (OB), La Mancha (LN), Toggenburg (TO) and Nubian (NU). The variation in milk production among all 11 breeds could explain the observations on fat and protein percentage to a certain degree because of the “concentration factor”. It appeared that when dairy goats produced a high volume of milk, the fat and protein contents of their milk decreased. Therefore, in this study fat and protein yields (g/d per doe) were derived from fat and protein percentage to take into consideration milk production. As shown in Figure 2 c and d, the differences in daily milk fat and protein yields among breeds were not as marked as those in fat and protein percentage. Alpine (AI), Nubian (NU), Sable (CC) and La Mancha (LN) goats had the highest fat yield because of their high milk production. Although Pygmy (PY) and Nigerian Dwarf (ND) showed the highest fat and protein contents, their fat and protein yields were the lowest because of their lowest milk volumes. Therefore, fat and protein yields for a specific volume of milk may be better parameters for price incentives than fat and protein contents, particularly when the milk is used for cheese manufacture, as it is the case for more than half of the goat milk worldwide [13]. In dairy cows, the payment system is already on yield of fat and protein, not content (percentage). Significant variations (P < 0.05) in SCC were also found among breeds (Figure 2 f), with Toggenburg (TO) and Nubian (NU) being the highest (5.69× and 5.34×105/ml, respectively), and Pygmy (PY) and Nigerian Dwarf (ND) being the lowest (1.11× and 1.3×105/ml, respectively). The mean SCC of milk from TO and NU were near the current regulatory limit of 1.0×106/ml for Grade “A” goat milk in the U.S. Paape et al. (2007) studied goat breed effect for a 5-year period and also found the highest SCC (6.5×105/ml) in Toggenburg milk [6]. A similar finding was reported by Sung et al. (1999), after investigating the milk quality of Alpine, Nubian, Saanen and Toggenburg in Taiwan. SCC in Toggenburg milk was the highest among the four breeds [17]. Figure 2 f further demonstrates that the major dairy breeds in the U.S. had a generally higher SCC while those low production breeds, such as Pygmy (PY), Nigerian Dwarf (ND), Experimental (EX) and Mixed (XX), tended to have lower SCC. The “concentration factor” mentioned above between fat or protein content and milk production did not appear to be applicable in SCC. Therefore, it would be wise to start a mixed herd of different breeds for a balanced volume, fat and protein content, and SCC of milk in meeting regulatory requirements and for cheese and yogurt manufacture purposes. Effect of stage of lactation (month) on fat, protein, SCC and production. Stage of lactation by month of the year is displayed in Figure 3. As demonstrated in Figure 3 a, the kidding pattern of most dairy goat herds in the U.S. was seasonal, kidding in March and drying off in November or December. Only 84 and 403 does were in lactation and tested in January and February, respectively. However, the number of does tested increased to almost 1,900 in March and was relatively constant from April through October. The number decreased in November as goats were dried off in late November and December. During year 2007, both fat and protein contents in goat milk were extremely high in January (5.14 and 4.45%, respectively) (Figure 3 b, c), probably because of the combination of the extremely low number of goats in test (n = 84, Figure 3 a) and the low milk production (2.8 kg/d per doe, Figure 3 d). As lactation advanced, fat and protein contents decreased to the lowest in June and July. Milk production increased and peaked in April (3.63 kg/d per doe) (Figure 3 d). When milk production started to decline significantly, fat and protein contents were found to increase again. As for SCC (Figure 3 e), an increasing trend (P < 0.05) was observed in the first eight months. SCC in January was the lowest at 1.74×105/ml, increased steadily until 6
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August, and reached the highest in November, even though SCC were relatively constant (P > 0.05) from August to December. It is well documented that SCC in goat milk increases as lactation advances. Gomes et al. reported the SCC value increased from 2.56×105/ml in the first month of lactation to 6.51×105/ml in the eighth month of lactation [18]. A recent report by Paape et al. further confirms the relationship between SCC and stage of lactation in dairy goats [6]. They examined the effect of days in milk (DIM) of lactating goats on SCC and found 2.5 to 4 times higher SCC in milk at 15 DIM than at 285 DIM depending on parity. The extremely high SCC in milk at 15 DIM could be resulted from a residual high SCC from colostrum because it was so close to kidding. They further pointed out that stage of lactation had a more significant impact on SCC in goat milk than in cow and sheep milk. In bulk tank goat milk (n = 2,582), elevated SCC was also observed in late months (August to December) of the year [11]. Therefore, year-round breeding and lactation programs for large herds would not only provide a stable supply of goat milk but also control SCC levels in goat milk throughout the year. Incentive payments for goat milk are needed for the producer to meet and improve health standard requirements for raw milk and to have optimum milk composition for high yield and quality of goat milk products such as cheese and yoghurt. Criteria used in Europe for the payment of bonus or penalty include coliform bacteria, total bacteria counts, SCC, pH, fat, protein, total solids, casein, antibiotic residue, and sediment. Any enforcement of the present or future cow milk SCC limits to goat milk is unrealistic, unfair and discriminatory. Separate goat milk standards, which take normal seasonal changes in goat milk composition and SCC into account, must be developed. Effect of parity on fat, protein SCC and production. Parity had a significant impact (P < 0.05) on fat content, protein content, milk production and SCC. As displayed in Figure 4 a, fat content in goat milk was similar (P > 0.05) among the first five parities but decreased significantly in parity 6 (P < 0.05). Minimal differences were found in protein content among the first five parities (P > 0.05) but like fat content a sharp decline (P < 0.05) in parity 6 was observed (Figure 4 b). It must be noted here that the number of test-day goats for parity 6 was extremely small (n = 848) in comparison with those in other parities. Goats in their first parity produced significantly less milk than in any other parities (P < 0.05), whereas goats in the third or fourth parity had the highest milk production (Figure 4 d). This observation was in agreement with report of Zeng and Escobar [7] on an Alpine herd. Figure 4 also shows an increasing trend in SCC (P < 0.05) as parity advanced, which was also reported by Wilson et al. [19], Contreras et al. [20] and Paape et al. [6]. Milk of goats in parity 1 had the lowest SCC of 3.0×105/ml. However, there was no significant difference (P > 0.05) between parities 2 and 3 or between parities 4 and 5. Parity 6 showed the highest SCC of 6.0×105/ml, which was significantly higher (P < 0.05) than that of any previous parity. After analyzing extensive data of dairy goats enrolled in the DHI program in the U.S., Paape et al. [6] concluded that advanced parity elevated SCC in milk significantly and suggested that much of the increase in SCC was attributed to non-infectious factors whereas some was due to increased intramammary infections with increased parity. The infection tends to be more common among goats in their third and fourth parities and during the later stages of lactation [16]. However, Zeng and Escobar [7] in a study with a limited number of Alpine goats (n = 120) did not observe any effect of parity on SCC. These observations in the current study suggest that it be practically important to consider culling goats after the fifth lactation as their milk fat and protein content decreased if their SCC in milk has increased, because such an increase may make it difficult to meet the Grade “A” goat milk requirements. Effect of states/regions on fat, protein and SCC in goat milk. Milk data of goats in this study represented almost all states, although the number of goats varied markedly from state to state. For this study, participating states were divided into five regions/areas, i.e., Wisconsin/Minnesota (WI/MN), Northeast, Southeast, West, and Southwest in a descending 7
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order of number of goats included. WI/MN had the highest number of goats participating in the DHI testing with 2190 does. Northeast was a close second at 2135 does. Southeast, West, Southwest regions had only 660, 536 and 507 goats, respectively. WI/MN and Northeast regions represented more than 70% of all goats included in this study. This distribution reflected the service areas of the laboratories contributing to this study. As shown in Figure 5 a, there were marked differences (P < 0.05) in fat percentage of goat milk among the regions. Goat milk of the Southwest region has the highest fat percentage (4.21%) while that of the WI/MN region had the lowest (3.65%). Goats in Southeast produced milk with the highest protein percentage (3.37%) (Figure 5 b), whereas goat milk in the other regions did not differ (P > 0.05) in protein percentage. Milk production varied significantly (P < 0.05) among regions, with Northeast being the highest (3.29 kg/d per doe) and Southeast and West being the lowest (2.83 kg/d per doe) (Figure 5 c). Significant variations in SCC (P < 0.05) were also demonstrated in Figure 5 d. As mentioned previously, WI/MN had the largest number of goats enrolled in the DHI program. Goat milk in the WI/MN region showed the highest SCC (4.65×105/ml), which was 37% higher than that in the Northeast region (3.39×105/ml). A similar finding in the same region was reported by Paape et al. [6], although their observed value was higher (>6.0×105/ml), indicating a significant improvement in herd management and udder health in the region in the last three years. Figure 4 further indicates that the heat stress in the Southeast or Southwest did not seem to be as large a factor as generally believed, as SCC in those two regions were close to that in Northeast. As pointed by Paape et al. [6] , variations in environmental temperature did not contribute to various SCC in goat milk in the U.S. However, the composite SCC of 3.92×105/ml (Table 1) in all regions and SCC in individual regions were less than half of the current Grade “A” limit for goat milk. Effect of herd size on fat, protein and SCC. As mentioned previously, most dairy goat herds in North America are small-scale and family-operated. The sizes of dairy goat enrolled in the DHI testing program varied tremendously, ranging from 1 to 487 goats per herd. As demonstrated in Figure 6 a b, in herds with fewer than 10 goats, milk had the highest fat and protein contents (P < 0.05). When herd size increased to more than 20 goats, milk fat tended to be lower (P < 0.05) than that in smaller herds. No differences in milk fat were observed between herd sizes of 21-50 and >50 goats. However, milk from herds of 21-50 goats had the lowest protein content and was lower than that from herds of >50 goats (P < 0.05). Figure 6 c shows that milk production increased significantly (P < 0.05) as herd sizes increased. Goats in herds of >50 tended to produce almost 8% more milk daily than those in herds of fewer than 10. However, a similar trend in SCC was also observed from Figure 5 d. SCC in goat milk increased significantly when herd size increased. Milk from large herds tended to have higher SCC than that from smaller herds. Milk from herds with >50 goats had 18% higher SCC than that of herds with fewer than 10 goats. This observation was in disagreement with the report of Norman et al. [21] in dairy cows. It is generally believed that better mastitis control in large cow herds is practiced than in small cow herds [21]. Herds with >50 does were considered commercial herds and would seem to have better herd management practices. However, opposite findings were observed in goat herds as in cow herds. Data in this study indicated that goats in smaller herds might have received more personal attention from the owners and thus better udder health management, resulting in lower SCC. Correlation coefficients between fat, protein, production and SCC of goat milk. Table 4 summarizes the correlation coefficients between fat, protein, production and SCC of goat milk using the composite data pooled from all three DHI laboratories/centers (n = 29,045). As expected, fat content in goat milk had a high positive correlation coefficient of 0.74 (P < 0.01) with protein content. Both milk fat and protein content were found to have a 8
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moderate negative correlation coefficient with milk production (-0.40 and -0.51, respectively). This finding partially explains the concentration factor mentioned previously and confirms the opposite observations on fat and protein contents and on milk production as shown in Figures 2 and 3. In addition, milk production showed a low negative correlation coefficient with SCC in milk (-0.13, P < 0.01), which was almost identical to the finding (-0.09) of Zeng et al. [9] after analysis of daily milk samples (n = 1,848) from an Alpine herd for one whole lactation (April to November). This current study also showed negligible correlations of fat or protein content with SCC (-0.04 and 0.02, respectively), confirming the results of Das and Singh [22]. They reported that SCC was correlated with neither milk fat content nor milk protein content. However, in a study of bulk tank goat milk in the mid-western and southeastern states, Zeng and co-workers [11] found much higher correlation coefficients between fat or protein content and SCC (0.35 and 0.31, respectively). CONCLUSIONS Statistical analysis of composite DHI data indicated that composition (fat and protein), SCC and production of goat milk were affected by many management and environmental factors. Marked variations in fat and protein contents and milk production were found among goat breeds, particularly among those less common dairy breeds, such as Sable, Mixed, Experimental, Nigerian Dwarf, and Pygmy. However, it seemed that milk of these breeds had lower SCC than that of the major breeds. Milk fat and protein contents did not show much variation in the first five parities, however, a sharp decline was observed in parity 6. SCC in milk increased steadily as parity increased. Significant differences in all variables were discovered among regions, probably because of different climates and management practices. Large herds of goats tended to have lower fat and protein contents in milk but higher milk production and SCC than small herds. The above observations suggest that it be practically imperative to consider culling goats after their fifth lactation when SCC is excessively high and that year-round breeding and lactation programs will help reduce SCC levels. All factors that contribute to variations in fat, protein, SCC and production of goat milk should be taken into consideration when establishing price incentive systems for goat milk. Monitoring composition, quality, production and SCC of goat milk on a year-round basis provides an important tool for small goat producers for herd management and makes dairy goat farming in the U.S. sustainable and profitable. ACKNOWLEDGEMENTS This study was funded by the 1890-Land Grand Institution Research Capacity Building Grant Program of USDA/SCREES (OKLX-SZ0410). Appreciation is given to Ms. E. Vasquez for her assistance in laboratory analysis and data collection. REFERENCES 1. PARK, Y. W., HYPO-ALLERGENIC AND THERAPEUTIC SIGNIFICANCE OF GOAT MILK. SMALL RUMINANT RESEARCH 1994, 14, 151-159. 2. SAHLU, T., L. J. DAWSON, T. A. GIPSON, S. P. HART, R. C. MERKEL, R. PUCHALA, Z. WANG, S.S. ZENG, AND A. L. GOETSCH, IMPACT OF ANIMAL SCIENCE RESEARCH ON U.S. GOAT PRODUCTION AND PREDICTIONS FOR THE FUTURE. JOURNAL OF DAIRY SCIENCE (SUBMITTED) 2008. 3. FAOSTAT, AVAILABLE AT: HTTP://FAOSTAT.FAO.ORG/SITE/569/DESKTOPDEFAULT.ASPX?PAGEID=569. IN 2007. 4. PMO, PASTEURIZED MILK ORDINANCE. PUBLIC HEALTH SERVICE, FOOD AND DRUG ADMINISTRATION, U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES. 2005. 5. MORONI, P.; PISONI, G.; RUFFO, G.; BOETTCHER, P. J., RISK FACTORS FOR INTRAMAMMARY INFECTIONS AND RELATIONSHIP WITH SOMATIC-CELL COUNTS IN ITALIAN
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DAIRY GOATS. PREVENTIVE VETERINARY MEDICINE 2005, 69, (3-4), 163-173. 6. PAAPE, M. J.; WIGGANS, G. R.; BANNERMAN, D. D.; THOMAS, D. L.; SANDERS, A. H.; CONTRERAS, A.; MORONI, P.; MILLER, R. H., MONITORING GOAT AND SHEEP MILK SOMATIC CELL COUNTS. SMALL RUMINANT RESEARCH 2007, 68, (1-2), 114-125. 7. ZENG, S. S.; ESCOBAR, E. N., EFFECT OF PARITY AND MILK PRODUCTION ON SOMATIC CELL COUNT, STANDARD PLATE COUNT AND COMPOSITION OF GOAT MILK. SMALL RUMINANT RESEARCH 1995, 17, (3), 269-274. 8. ZENG, S. S.; ESCOBAR, E. N., EFFECT OF BREED AND MILKING METHOD ON SOMATIC CELL COUNT, STANDARD PLATE COUNT AND COMPOSITION OF GOAT MILK. SMALL RUMINANT RESEARCH 1996, 19, (2), 169-175. 9. ZENG, S. S.; ESCOBAR, E. N.; POPHAM, T., DAILY VARIATIONS IN SOMATIC CELL COUNT, COMPOSITION, AND PRODUCTION OF ALPINE GOAT MILK. SMALL RUMINANT RESEARCH 1997, 26, (3), 253-260. 10. ZENG, S. S.; ESCOBAR, E. N.; HART, S. P.; HINCKLEY, L.; BAULTHAUS, M.; ROBINSON, G. T.; JAHNKE, G., COMPARATIVE STUDY OF THE EFFECTS OF TESTING LABORATORY, COUNTING METHOD, STORAGE AND SHIPMENT ON SOMATIC CELL COUNTS IN GOAT MILK. SMALL RUMINANT RESEARCH 1999, 31, (2), 103-107. 11. ZENG, S. S.; POPHAM, T.; ESCOBAR, E. N., SEASONAL VARIATION OF SOMATIC CELL COUNT AND CHEMICAL COMPOSITION IN BULK TANK GOAT MILK. DAIRY, FOOD ENVIRONMENT SANITARIANS 1999, 19, (10), 685-689. 12. ZENG, S. S., COMPARISON OF GOAT MILK STANDARDS WITH COW MILK STANDARDS FOR ANALYSES OF SOMATIC CELL COUNT, FAT AND PROTEIN IN GOAT MILK. SMALL RUMINANT RESEARCH 1996, 21, (3), 221-225. 13. PIRISI, A.; LAURET, A.; DUBEUF, J. P., BASIC AND INCENTIVE PAYMENTS FOR GOAT AND SHEEP MILK IN RELATION TO QUALITY. SMALL RUMINANT RESEARCH 2007, 68, (1-2), 167-178. 14. HAENLEIN, G. F. W., PAST, PRESENT, AND FUTURE PERSPECTIVES OF SMALL RUMINANT DAIRY RESEARCH. JOURNAL OF DAIRY SCIENCE 2001, 84, (9), 2097-2115. 15.
SAS SAS USER'S GUIDE: STATISTICS, SAS INSTITUTE INC.: CARY, NC, 1999.
16. MILLER, R. H., H.D. NORMAN, AND L.L.M. THORNTON SOMATIC CELL COUNTS OF MILK FROM DAIRY HERD IMPROVEMENT HERDS DURING 2007; ARS-USDA: BELTSVILLE, MD 20705-2350. ALSO AVAILABLE AT: HTTPS://AIPL.ARSUSDA.GOV/PUBLISH/DHI/CURRENT/SCCRPT.HTM, 2008. 17. SUNG, Y. Y.; WU, T. I.; WANG, P. H., EVALUATION OF MILK QUALITY OF ALPINE, NUBIAN, SAANEN AND TOGGENBURG BREEDS IN TAIWAN. SMALL RUMINANT RESEARCH 1999, 33, (1), 1723. 18. GOMES, V.; MELVILLE PAIVA DELLA LIBERA, A. M.; PAIVA, M.; MADUREIRA, K. M.; ARAUJO, W. P., EFFECT OF THE STAGE OF LACTATION ON SOMATIC CELL COUNTS IN HEALTHY GOATS (CAPRAE HIRCUS) BREED IN BRAZIL. SMALL RUMINANT RESEARCH 2006, 64, (1-2), 30-34. 19. WILSON, D. J.; STEWART, K. N.; SEARS, P. M., EFFECTS OF STAGE OF LACTATION, PRODUCTION, PARITY AND SEASON ON SOMATIC CELL COUNTS IN INFECTED AND UNINFECTED DAIRY GOATS. SMALL RUMINANT RESEARCH 1995, 16, (2), 165-169. 20. CONTRERAS, A.; PAAPE, M. J.; MILLER, R. H., PREVALENCE OF SUBCLINICAL INTRAMAMMARY INFECTION CAUSED BY STAPHYLOCOCCUS EPIDERMIDIS IN A COMMERCIAL DAIRY GOAT HERD. SMALL RUMINANT RESEARCH 1999, 31, (3), 203-208. 21.
NORMAN, H. D.; MILLER, R. H.; WRIGHT, J. R.; WIGGANS, G. R., HERD AND STATE MEANS
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FOR SOMATIC CELL COUNT FROM DAIRY HERD IMPROVEMENT. JOURNAL OF DAIRY SCIENCE 2000, 83, (12), 2782. 22. DAS, M.; SINGH, M., VARIATION IN BLOOD LEUCOCYTES, SOMATIC CELL COUNT, YIELD AND COMPOSITION OF MILK OF CROSSBRED GOATS. SMALL RUMINANT RESEARCH 2000, 35, (2), 169-174. Formatted: Line spacing: single
Formatted: Line spacing: single
11
TABLE 1. Leading countries of dairy goat inventories in the world in 2006 (in million). Country
Heads of dairy goat
India
29.7
Sudan
23.7
Bangladesh
17.7
Iran, Islamic Rep of
12.7
Pakistan
6.2
Indonesia
5.3
Brazil
4.5
Greece
4.3
Tanzania, United Rep of
2.6
Niger
2.5
Turkey
2.4
Algeria
2
Kenya
1.9
Burkina Faso
1.9
Saudi Arabia
1.6
China
1.4
Yemen
1.3
Nepal
1.3
Spain
1.3
Egypt
1.2
Developed Countries
10.4
Developing Countries
150.2
World total
160.6 Formatted: Line spacing: single
Source: http://faostat.fao.org/site/569/DesktopDefault.aspx? PageID=569
12
TABLE 2. Leading states of dairy goat inventories in the United States in 2007. State Wisconsin California Texas Iowa Missouri New York Pennsylvania Ohio Indiana Colorado Washington Oklahoma Michigan Minnesota North Carolina Arkansas Kentucky Tennessee Oregon Illinois US Total
Head 33000 30000 25000 19000 13000 13000 13000 9200 9100 9000 8400 8000 7900 6600 6000 5900 5900 5800 5700 4900 305000
Source: Sheep and Goats (Mt An 5-2, February 2008), Agricultural Statistics Board, National Agricultural Statistics Service (NASS) of United States Department of Agriculture (USDA), Washington, DC.
13
TABLE 3. Overall means of major milk constituents (%), somatic cell count (SCC，×105/ml) and milk production (kg/d per doe). Variable Fat Protein SCC Milk production
Mean 3.81 3.15 3.92 3.13
SD 1.29 0.71 0.47 1.44
Range 1.00-9.00 1.00-8.50 0.13-119 0.05-12.23
n 29,036 29,045 27,318 29,045
14
TABLE 4. Correlation coefficients between fat, protein, somatic cell count (SCC) and milk production (P < 0.01).
Fat Protein Milk production
Protein 0.74
Milk production -0.40 -0.51
SCC -0.04 0.02 -0.13
15
5
FIGURE 1. Cumulative distribution function plot of somatic cell count (SCC, ×10 /ml) in goat
milk (n = 29,045).
60.00% 50.00% 40.00% 30.00% 20.00% 10.00% 0.00% 4.0
>7.5
>10
SCC
16
FIGURE 2. Effect of breed on fat and protein contents (%), fat and protein yields (g/d per doe), milk production (kg/d per doe) and somatic cell count (SCC, ×105 /ml) in goat milk. Sable (CC, n = 111); Toggenburg (TO, n = 1,790); Alpine (AI, n = 10,005); Sannen (EN, n = 4,025); Oberhasli (OH, n = 1,178); La Mancha (LN, n = 3,314); Mixed (EX, n = 1,668); Nubian (NU, n = 4,449); Experimental (XX, n = 1,483); Pygmy (PY, n = 162); Nigerian Dwarf (ND, n = 851). a,b,c,d,e,f,g,h Means with different letters differed (P < 0.05) according to LSD.
2a
2b
7.00
5.00
a
6.50
b
4.50
a
a
PY
ND
6.00
5.00
c
4.50 e
4.00 3.50
h
CC
TO
c
d
f
g
g
h
Protein (%)
Fat (%)
5.50
4.00
b d
3.50
c
e 3.00
g
f
f
f
TO
AI
EN
OH
h 2.50
3.00 2.50
2.00 AI
EN
OH
LN
EX
NU
XX
PY
ND
CC
Breed 2d
2 c 140.00
Fat (g/d per doe)
120.00
c 100.00
a,b
a,b
b
a
100.00 c
c
d
80.00 e f
60.00
b,c d
e,f
c
c d,e
f
80.00 60.00
g h
40.00
TO
AI
EN
OH
LN
EX
NU
XX
PY
ND
CC
TO
AI
EN
OH
Breed
LN
EX
2f
4.50
a
6.00
b d
d
3.00
PY
ND
f
e
PY
ND
a
c d
XX
7.00
a
3.50
NU
Breed
SCC (105 cells/ml)
Milk production (kg/d per doe)
XX
0.00 CC
4.00
NU
20.00
40.00
2e
EX
120.00 a,b
a
Protein (g/d per doe)
a,b
LN Breed
e
e f
2.50 2.00 1.50
g
g
PY
ND
5.00 4.00
b
b
b,c c d
d
3.00
d
2.00 1.00
1.00 0.50
0.00 CC
TO
AI
EN
OH
LN Breed
EX
NU
XX
CC
TO
AI
EN
OH
LN
EX
NU
XX
Breed
17
FIGURE 3. Effect of stage of lactation (month) on fat content, protein content, milk production (kg/d per doe) and somatic cell count (SCC, ×105/ml) in goat milk. Jan (n = 84); Feb (n = 403); Mar (n = 1,898); Apr (n = 2.900); May (n = 3,171); Jun (n = 3,530); Jul (n = 3,591); Aug (n = 3,317); 9 (n = 3,117); Oct (n = 3,164); Nov (n = 2,472); Dec (n = 1,389). a,b,c,d,e,f,g,h,i Means with different letters differed (P < 0.05) according to LSD. 3b
4000
3530 3591
3500
3171 2900
Number of Does
3000
3117 3164
5.00 b
2472
2500 1898
2000
1389
1500
4.50
c
c,d
4.00
d e f,g
1000 500
5.50 a
3317
Fat (%)
3a
403
g,h
Jan Feb Mar Apr May Jun
Jul
3.00 Jan Feb Mar Apr May Jun
Jul
Aug Sep Oct Nov Dec
a
4.00 b
b,c c e g
c
f g,h
3.00
i
h,i
i
2.50 Jul
Aug Sep Oct Nov Dec
Month
a
3.70 a,b
3.50
b
a b
3.30
c c
3.10 d 2.90
d
d e
2.70
e
Jan Feb Mar Apr May Jun
Jul
Aug Sep Oct Nov Dec
Month
7.00 6.00 a
SCC (105 cells/ml)
3.90
2.50 Jan Feb Mar Apr May Jun
3e
Milk production (kg/d per doe)
Protein (%)
3d
5.00
3.50
Aug Sep Oct Nov Dec
Month
Month
4.50
h
84
0
3c
e,f g,h
3.50
d
a
a
a a
5.00 b
4.00
b,c
3.00 2.00
d,e
c,d e
d,e
f
1.00 0.00 Jan Feb Mar Apr May Jun
Jul
Aug Sep Oct Nov Dec
Month
18
FIGURE 4. Effect of parity on fat content, protein content, milk production (kg/d per doe) and somatic cell count (SCC, ×105/ml) in goat milk. Parity 1 (n = 11,543); Parity 2 (n = 7,459); Parity 3 (n = 4,528); Parity 4 (n = 2,989); Parity 5 (n = 1,669); Parity 6 (n = 848). a,b,c,d Means with different letters differed (P < 0.05) according to LSD. 4b
4.00 3.90
Fat (%)
a 3.80
a
a
b
3.70
3.30 3.20
a a
Protein (%)
4a
3.60
a
a,b
a,b
3.10 d 3.00 2.90
3.50
2.80 1
2
3
4
5
6
1
2
3
Parity 4d
3.70 a
3.50
4
5
6
Parity
8.00 a
a b
b 3.30
b
3.10 2.90 c
SCC (105 cells/ml)
Milk production (kg/d per doe)
4c
b,c
c
b
6.00
4.00
c
c
2
3
b
d
2.00
2.70 2.50
0.00 1
2
3
4 Parity
5
6
1
4
5
6
Parity
19
FIGURE 5. Effect of region on fat and protein contents (%), fat and protein yields (g/d per doe), milk production (kg/d per doe) and somatic cell count (SCC, ×105/ml) in goat milk. Northeast (N.E., n = 10,028); Southeast (S.E., n = 3,628); Southwest (S.W., n = 2,337); West (W., n = 3,127); Wisconsin/Minnesota (WI/MN, n = 9,916). a,b,c,d Means with different letters differed (P < 0.05) according to LSD. 5a
5b
4.40
a
3.40
a 4.20
3.30
Fat (%)
3.80
c
c
d 3.60
Protein (%)
b 4.00
3.40
b
3.20
c
c
3.00 2.90
3.20
2.80 N.E.
S.E.
S.W.
W.
WI/MN
N.E.
S.E.
Region
3.40
5d
a b
3.20 c 3.00 d
S.W.
W.
WI/MN
Region
d
2.80 2.60
6.00 5.00
SCC (105 cells/ml)
Milk production (kg/d per doe)
5c
c
3.10
a b
4.00
d
c,d
N.E.
S.E.
c
3.00 2.00 1.00
2.40
0.00 N.E.
S.E.
S.W. Region
W.
WI/MN
S.W.
W.
WI/MN
Region
20
FIGURE 6. Effect of herd size on fat and protein contents (%), fat and protein yields (g/d per doe), milk production (kg/d per doe) and somatic cell count (SCC, ×105/ml) in goat milk. 1 (herd size = 1~10, number of herds = 150, n = 3,814); 2 (herd size = 11~20, number of herds = 100, n = 6,723); 3 (herd size = 21~50, number of herds = 29, n = 3,832); 4 (herd size >50, number of herds = 21, n=14,667). a,b,c,d Means with different letters differed (P < 0.05) according to LSD. 6a
6b
4.40
3.40
a
a 3.30
4.20
Protein (%)
Fat (%)
b b
4.00 3.80
c
c
3.60
3.20
c
3.10 d 3.00 2.90
3.40
2.80 1
2
3
4
1
2
Herd size 6d
3.30 3.20
a,b
a 4.00
b 3.10 3.00
4
5.00
a
SCC (105 cells/ml)
Milk production (kg/d per doe)
6c
3 Herd size
c
2.90
c
b
b
3.00 2.00 1.00
2.80 2.70
0.00 1
2
3 Herd size
4
1
2
3
4
Herd size
21
