The Relationship between Linear Type Traits and ...

Reprod Dom Anim 43, 599–605 (2008); doi: 10.1111/j.1439-0531.2007.00962.x ISSN 0936-6768

The Relationship between Linear Type Traits and Fertility Traits in High-yielding Dairy Goats M Mellado1, J Mellado1, M Valencia2 and W Pittroff3 1 Department of Nutrition and Foods, Universidad Autonoma Agraria Antonio Narro, Saltillo, Me´xico; 2Instituto de Ciencias Agrı´colas, Universidad de Guanajuato, Irapuato, Me´xico; 3Department of Animal Science, University of California, Davis, CA, USA

Contents Reproductive data collected from 13 medium-size goat farms in central Mexico (582 goats), were used to investigate if linear type traits influenced reproductive performance of high-yielding dairy goats. Data were analysed using multiple stepwise forward logistic regressions. Goats with the higher scores for strength were 1.43 times more likely (p < 0.05) to have larger litters (1.49 vs 1.39) than goats with lower strength. Goats approaching level rump angles were 1.68 times more likely (p < 0.01) to have larger litters, compared with goats with extremely sloped rump angles (1.48 vs 1.37). Goats with rear legs nearly straight (posty) in hock tended (p < 0.08) to presented larger litters than goats with rear legs slightly angled (sickled) in hock (1.49 vs 1.38). Less pronounced rump angle was favourable associated (p < 0.05) with litter weight (4.88 vs 4.53 kg) compared with goats with low pin bones. Goats with poorer udder texture were 1.42 more likely (p < 0.05) to have heavier litters than goats with good udder texture. Goats with faulty mammary system tended (p < 0.07) to have heavier litters than goats with good mammary system. Increasing udder height was associated (p < 0.05) with increasing number of services per conception. Goats with good fore udder attachment and non-refined heads were at reduced risk (p < 0.05) for stillbirths. Goats with stronger median ligament were 65% less likely (p < 0.05) to lose their foetuses than those with looser udder support. Our findings indicate that a greater litter size and litter weight is expected in goats as rump angle becomes less sloped. This study showed that a relationship exists between strength of goats and litter size, and that some traits linked to high milk yield were antagonist to some reproductive traits.

Introduction Linear traits (subjective visual characteristics assessment of animals by classifiers) in dairy goats are functional traits that allow the producer to know where their does are ‘weak’ and where their does are ‘strong’, therefore this information is widely used to advertize does and promote herds. However, because of the moderate to high heritability of these traits (Luo et al. 1997), these numbers are a valuable tool in breeding programmes for the prediction of some productive traits in dairy cattle such as longevity (Vollema and Groen 1997), udder health (Thomas et al. 1984), calving ease (Cue et al. 1990), feet and leg problems (Boelling and Pollott 1998) and fertility (Royal et al. 2002). Linear traits are currently included in the genetic evaluations of a variety of breed of goats in the United States of America (Wiggans and Hubbard 2001). Despite the wide use of evaluations for type in goats, little is known about the association between body conformation and some reproductive traits in this

species. In dairy cows, it has been suggested that high pin bones negatively affect fertility mainly through longevity (Caraviello et al. 2004; Sewalem et al. 2004). The reasoning is that, with an upward angle, the reproductive tract is more susceptible to infection because drainage of the vagina (Astiz et al. 2002) and passage of the calf at parturition trough the birth canal is more difficult (Cue et al. 1990). Data of Perez-Cabal and Alenda (2002) suggest that cows with an intermediate rump angle had lower culling rates than cows at the extremes (high and low pin bones). Other studies have shown that fertility (success at AI; Larroque et al. 1999) and luteal activity (Royal et al. 2002) are unfavourably correlated with hip traits. However, several studies have found no evidence between fertility and rump traits in dairy cattle (Pryce et al. 2000; Wall et al. 2005). Additional studies with dairy cows indicated that poor legs and feet are negatively associated with fertility (Melendez et al. 2003), because oestrus behaviour is impaired by faulty legs (Van Eerdenburg et al. 2002) and lameness is associated with delayed ovarian activity (Garbarino et al. 2004). On the basis of these findings in dairy cattle, we tested the hypothesis that some linear type traits are associated to some fertility traits in high-yielding goats.

Materials and Methods Experimental animals Data were collected from 582 Saanen and Alpine goats in 13 well-managed progressive commercial herds in central Mexico (longitude: 10036¢W; latitude: 2041¢N), which kidded between January 2003 and March 2004. These herds were characterized by a medium-size operations (50–240 animals), with a median of 89 animals, and high milk yields per lactation (range from 600 to 900 kg per animal). Because all farms belonged to a local society and were attended by the same nutritionist and veterinarian, there were no clear peculiarities with respect to husbandry, nutrition and management on the farms in this study. Goats in these operations derived from imported stock from the United States of America. Most of the sires used for natural mating were also imported from the USA. Goats were housed in loose housing systems in large, completely covered open sheds pens. In all herds, goats were machine-milked twice daily and follow strict hygiene measures. All goats were identified by ear tags.

 2008 The Authors. Journal compilation  2008 Blackwell Verlag

600

M Mellado, J Mellado, M Valencia and W Pittroff

Goats were fed Alfalfa hay, soybean meal and cereal grains, twice a day according to the American National Research Council recommendations (NRC 1981). All farms were serviced by one veterinarian whose herd health programme consisted of routine two- to four weekly visits, in which goats were vaccinated against endemic diseases (Clostridium perfringins and Clostridium tetani) and examined for postpartum checks (occurrence of vaginal discharges or retained placenta), pregnancy diagnosis, mastitis tests and illness indicated by the farmers. Milk yield and reproduction records were computer recorded by the attending veterinarian. In all herds breeding was mostly done by hand-mating, exposing goats to fertile mature bucks of their same breed from May to March. Does were allowed to breed for the first time at 6–9 months of age. Pregnancy diagnosis was performed by transrectal ultrasonography 30–40 days postservice. A requirement for inclusion in the study was that farms have over 50 milking goats, they were in the same zone (all farms were in a radius of 30 km), participation in a milk recording scheme, similar health and feeding programs, linear body traits evaluated by the same judge and strict recording of reproductive performance. Data description Data collected included those depicted in Table 1. Linear appraisal scoring was made in lactating goats (at any stage of lactation) by a licensed ADGA judge from the United States of America. The linear appraisal system used in this study corresponded to the standard scoring established by the American Dairy Goat Association (1993). These linear traits were scored between biological extremes on a continuous scale (1–50). Final scores range from 50 to 99. For structural traits, a scale one to six was used to describe animals rated as excellent (1), very good (2), good plus (3), acceptable (4), fair (5) and poor (6), respectively. Type records were adjusted for doe’s age at appraisal. Regarding the reproductive traits, natural-service dates were recorded for each individual doe during the breeding season (year-round, except April). Additional data collected for each goat were: dystocia (yes, no), stillbirth (yes, no), abortion (yes, no), litter size (kids born⁄doe kidding; including still-born kids), litter weight (weights of kids within 24 h of birth) and services per conception. For aborted foetuses the entire foetus and placenta were submitted to a veterinary diagnostic laboratory. Abortions in these dairy operations were not caused either by Brucella melitensis or Chlamydia psittaci. Stillbirth was defined as the birth of a dead kid or a kid dead within 24 h after parturition. Statistical analysis For statistical analysis goats were classified into one of two categories of body traits: those above or below average values for each body character included in this study (Table 1). Adjustments were made to balance the number of observations per group,

Table 1. Descriptive statistics for body and reproductive traits used in the analysis, for high-yielding Saanen and Alpine goats in central Mexico Mean ± SD Saanen USA

Point for classes separation

Traits

Mean ± SD

Stature Strength Dairyness Rump angle Rump width Rear legs (side view) Fore udder attachment Rear udder height Rear udder arch Medial ligament Udder depth Teat placement (rear view) Teat diameter Udder lateral view Head Shoulder front legs Rear legs Hoofs Back Foot angle Udder texture General appearance Dairy character Body size and capacity Mammary system Final score Litter size Litter weight at birth (kg) Services per conception Stillbirths (%) Abortions (%) Dystocia (%)

23.05 27.8 33.7 29.1 27.5 27.4 26.6 34.8 19.9 26.8 29.8 15.0

± ± ± ± ± ± ± ± ± ± ± ±

6.4 3.3 3.1 4.9 3.7 3.9 6.4 6.2 4.3 5.1 7.7 6.9

28.4 29.0 34.3 31.2 31.0 28.0 34.9 35.6 27.8 27.0 34.3 18.4

6.3 3.7 3.4 5.5 4.2 3.1 3.8 5.9 6.0 4.6 6.7 5.9

23 27 34 28 27 27 26 35 19 26 29 13

17.7 22.6 2.5 3.3 3.1 2.4 4.2 2.0 2.3 2.3 2.8 1.8 1.8 3.4 81.5 1.4 4.7

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

7.5 3.6 0.7 1.0 0.9 1.0 0.9 0.9 1.1 1.1 0.8 0.8 0.8 1.1 4.7 0.5 1.9

22.6 ± 6.1

15 22 2 3 3 2 3 2 2 2 2 2 2 3 84 – –

1.13 ± 0.34 4.2 4.0 0.3

± ± ± ± ± ± ± ± ± ± ± ±

86.3 ± 3.2

– 1 or 0 1 or 0 1 or 0

Values for Saanen goats in the United States (http://www.ADG.org).

therefore, in some parameters the cut point slightly differs from the mean. The null hypothesis that odds of prolificacy (one kid vs. two or more), litter weight, services per conception and risk of certain reproductive disorders is the same in goats classified as above or below average for different body trait was tested by using multiple stepwise forward logistic regressions (PROC LOGISTIC; SAS 9.1, 2004). The effect of herd, breed of dam and mating season were also included in the model. Mating months were categorized into four seasons: spring (May–June), summer (July–September), fall (October–December) and winter (January–March). A variable had to be significant at the 0.10 level before it could enter the model. A variable remained in the model when its significance level was p < 0.7. For all analyses, values of p < 0.05 were considered significant. To assess the goodness-of-fit of the logistic regression model, the Hosmer Lemeshow statistic was calculated in the logistic procedure in SAS Institute (2004). Potential factor (Table 1) associated with reproductive performance of goats were included in the model as independent variables. For reproductive traits, the resulting values (odds ratios) were then interpreted as a multiplicative measure

 2008 The Authors. Journal compilation  2008 Blackwell Verlag

Linear Type Traits and Fertility in Goats

601

of risk that range from 0 to infinity. An odd ratio of ‘1’ indicates that the factor examined does not alter risk. Odds ratios >1 are predisposing and imply a direct association. Odds ratios 1 offspring. Strength was associated with an increase likelihood of multiple offspring. The strongest goats were 43% more likely (p < 0.05) to produce multiple births than medium to weak goats. This response could be due to the fact that goats with greater

strength, compared with frail animals, will have a higher capacity to store nutrients and energy, which can be mobilized if needed, as is the case during lactation or ovulation, i.e., may have a greater metabolic buffering capacity. Moreover, strength present a strong negative genetic correlation with dairyness (Wiggans and Hubbard 2001), which implies that goats with a strong structure produce less milk, and thus are capable of funnelling greater amounts of nutrients for the reproductive effort. In dairy cows, animals with the highest scores for stature, size, chest width and loin strength have more chances of surviving than a cow in the reference class (Schneider et al. 2003). Body volume traits (e.g., stature, body depth) have been shown to be related to calving interval in dairy cattle (Haile-Mariam et al. 2004). Likewise, live weight at joining, which reflects to some extent strength, has been implicated in the increment of multiple offsprings in ewes (Hall et al. 1994) and goats (Constantinou 1989). Mating early in the year tended (p < 0.06) to increase litter size (Table 2). The season effect on litter size of goats in this study is similar to that of dairy confined goats located in other temperate regions of the world (Burguete et al. 1998; Mellado et al. 2006). Goats with the less sloped rump angle were 1.68 times more likely (p < 0.01) to have multiple offspring than goats with markedly sloped rump angles. Predicted probabilities of multiple kiddings due to rump angle are shown in Fig. 1. The probability of multiple kids per goat kidding increased linearly as pin bones got closer to the hip bones in a horizontal plane. The lack of an asymptotic curve probably was due to the fact that, in general, goats do not present high pin bones as in some dairy cows, where, in some cases, pin bones tilt the vaginal canal, causing it to lie at an angle rather than lying flat. In goats it is rare to find a goat approaching level rump angles. This response differs from cows, where pin bone setting shows an intermediate ideal, because cows with extremely high or low hips are at higher risk of being culled than cows with an intermediate phenotype (Schneider et al. 2003). Some studies in dairy cattle have found little or no relationship between rump traits and fertility (Pryce et al. 2000; Perez-Cabal and Alenda 2002; Wall et al. 2005). On the other hand, rump angle and width have been shown to have an unfavourable

Table 2. Summary of logistic regression model of the influence of body traits associated with litter size at kidding in high-yielding dairy goats under intensive conditions in central Mexico

Strength 27 Mating season Spring vs winter Summer vs winter Fall vs winter Rump angle 28 Foot angle 2

95% CI (OR)

0.7

Litter size (Mean ± SD)

Odds ratio

290 278

1.39 ± 0.47 1.49 ± 0.49

1.0 1.43

1.01–1.52

53–156 157–156 216–156

1.56 vs 1.36 1.48 vs 1.36 1.41 vs 1.36

2.12 1.58 1.35

1.11–4.06 0.99–2.53 0.87–2.1

259 309

1.37 ± 0.47 1.48 ± 0.49

1.0 1.68

1.09–2.59

0.01

321 247

1.38 ± 0.48 1.49 ± 0.48

1.0 1.45

0.93–2.27

0.08

n

p-value

0.04 0.06

Probability of litter weight > 3.8 kg

0.6 Probability

Item

0.8

0.5 0.4 0.3 Probability > 1 Offspring per kidding

0.2 0.1 0 10

15

20

25

30 35 Rump angle

40

45

50

Fig. 1. Estimated probabilities of litter size and litter weight for high yielding goats for different rump angle scores

 2008 The Authors. Journal compilation  2008 Blackwell Verlag

602

M Mellado, J Mellado, M Valencia and W Pittroff

correlation (direct and maternal) with calving ease in dairy cows (Cue et al. 1990). Investigations in the mechanisms of prolificacy in small ruminants indicate that differences among breeds involve follicular development, ovulation rate, uterine capacity, embryonic survival and foetal survival (Fahmy 1990; Waldron and Thomas 1992). Thus, we know of no biological explanation for this observation other than perhaps goats with a downward rump angle are expected to be less prone to uterine infections as drainage from the vagina would be more effective. This drainage could also apply to the semen, as most sperm cells deposited in the reproductive tract are drained to the exterior in cervical mucus (Hawk 1987), and possibly a lower sperm population in doe reproductive canal could be the cause of smaller litters in goats with extremely sloped rump angles. Compared with goats with excellent or very good foot angle, goats with fair to poor foot angles tended (p = 0.08) to have more than one kid per parturition. This result is intriguing because good foot angle allow goats to walk easily and minimize joint problems. As the shape of the rump affects leg set, it could be that goats with the less pronounced rump angles (more prolific) may result in steep foot angles and consequently be classified as fair to poor. In dairy cattle it has been reported that as foot angle becomes steeper, the number of inseminations per pregnancy increases (Shapiro and Swanson 1991). These results disagree with previous studies in dairy cows where feet scores are favourably correlated with fertility (Haile-Mariam et al. 2004; Wall et al. 2005) and longevity (Schneider et al. 2003; Sewalem et al. 2004, 2005). Heritability for foot angle is very low (Rogers and McDaniel 1989) and any relationship of this trait with reproductive traits that we or others have observed is probably of little or no economic consequence. Litter weight Goats with the less sloped rump angle were 1.5 times more likely (p < 0.05) to have heavier litters at kidding than goats with pin bones far down the hip bones (Table 3). As rump angle had also an important influence on litter size, the evidence of a relationship between rump angle and litter weight was not surprising,

Table 3. Logistic regression model of body traits associated with litter weight at kidding in dairy goats under intensive conditions in central Mexico

Item

n

Herd Rump angle 28 309 Udder texture 2 300 Mammary system 3 289

Litter weight (Mean ± SD), kg

Odds ratio

95% CI (OR)

Range = 3.82–4.87

p-value

given the strong association between litter size and litter weight in small ruminants (Freetly and Leymaster 2004). Udder traits had an important influence on litter weight. Goats with suboptimum udder texture were 1.5 more likely to have heavier litters as were goats graded as very good or excellent for this trait (Table 3). Likewise Goats with the lower scores for mammary system were 1.4 times more likely to have heavier litters than goats with good mammary glands. Milk yield in goats is positively related to shape and structure of the udder (Mellado et al. 1991; Peris et al. 1999). Thus, it is assumed that larger litters in goats with deficient udders are a reflection of a lower milk production capacity, which would allow the goats to diverted more energy for the reproduction effort than for milk synthesis. In dairy cattle both dairy character and dairyness presented unfavourable genetic correlations with fertility (Dadati et al. 1986). Services per conception Services per conception differed (p < 0.01) among herds, even though the difference was numerically small (Table 4). Increasing udder height was associated (p < 0.05) with increasing number of services per conception. This finding is difficult to explain because the underlying causes of increasing services per conception is a complex combination of several physiological and management factors (Lucy 2001). However, Berry et al. (2004) also found that dairy cows with higher shallow udders required more services per conception. Reproductive disorders Table 5 lists the factors which affected the likelihood of stillbirths. Goats with greater scores for fore udder were less than half as likely (p < 0.05) to have stillbirths, as were goats with poor fore udder conformation. In dairy cows, following parity, dystocia is the next most influential predictor of whether a calf would be alive or stillborn (Meyer et al. 2000; Eriksson et al. 2004). In this study complications during labour were practically non-existing, which reaffirm previous findings in the sense that stillbirth in goats is not a dystocia-related problem (Mellado et al. 2006). In goats, an important risk factor associated with stillbirths is increasing age of doe (Osuagwuh 1991; Mellado et al. 2006), but the predominant goats in this study were young. Stillbirth is the consequence of a constellation of pathophysiologic conditions and the cause of death for Table 4. Logistic regression model of body traits associated with services per conception in dairy goats under intensive conditions in central Mexico

0.01 Item

4.53 ± 1.86 4.88 ± 2.04

1.0 1.46

4.51 ± 1.95 4.90 ± 1.98

1.0 1.42

1.06–1.89

0.02

4.66 ± 2.03 4.78 ± 1.90

1.0 1.38

0.95–2.02

0.07

1.01–2.10

n

Serv⁄conception (Mean ± SD), n

Odds ratio

95% CI (OR)

p-value

1.02 1.33

1.0 3.11

0.79–12.21

0.01

1.10 ± 0.31 1.16 ± 0.37

1.0 1.70

1.01–2.89

0.05

0.03 Herd Lowest 68 Highest 97 Udder height 28 292

 2008 The Authors. Journal compilation  2008 Blackwell Verlag

Linear Type Traits and Fertility in Goats

603

Table 5. Logistic regression model of body traits associated with the occurrence of stillbirth in dairy goats under intensive conditions in central Mexico

Item Fore udder 26 Herd Head 2

Odds ratio

95% CI (OR)

0.06 0.03 Range = 0.0–0.10

1.0 0.35

0.15–0.82

0.02 0.01

0.07 0.02

1.0 0.24

0.09–0.60

0.002

n

Stillbirth

311 271

282 300

p-value

Conclusions

a large proportion of stillborn offspring remains unknown (Meijering 1984). In our particular case, we do not find a biological explanation for influence of udder traits on the occurrence of stillbirths, other than perhaps goats with better fore udder attachment produced more milk, and higher levels of milk production could restrict the amount of nutrients reaching the foetuses. On the other hand, those goats classified poorly regarding the head shape, were at decrease risk of presenting stillbirth, compared with goats with more feminine and harmonious head. It has been considered that shape of head has more to do with breed character than with function, but beauty of eyes, nose, ears and refinement of overall form possibly decreases the ability to consume large amounts of forage with ease, as oral morphology has a bearing on diet selection in goats (Mellado et al. 2007). Abortions were more common in goats with better udder height, compared with goats with lower scores for this trait (Table 6). Goats with stronger median ligament were 65% less likely to lose their foetuses than those with looser udder support. In dairy cows it has been observed a higher milk yield in cows with looser udder attachment (Norman et al. 1988; Brotherstone 1994). Thus, in this study stronger udder support might be related to lower milk yield of goats, which could have decreased nutritional stress and, consequently, decreased risk of abortion. As infectious causes of abortion were not detected in these goat operations, it is likely that spontaneous abortions were caused by stress or nutrition, as it has been observed in well-managed goat flocks (Engeland et al. 1998; Bath et al. 2005). As the corpus luteum in goats produces all the progesterone needed to maintain

Table 6. Logistic regression model of body traits associated with the occurrence of abortion in dairy goats under intensive conditions in central Mexico

Item

n

Herd Udder height 35 290 Median ligament 26 267

Abortion

Odds ratio

pregnancy, abortions can result from luteolysis when prostaglandin production is triggered by stress or malnutrition. These data then suggests that stronger udder support lead to lower odds of non-infection abortion. Perhaps this is so because goats with stronger udder ligaments produce less milk and possess greater body energy reserves, which would result in greater investment for the development of their foetuses.

95% CI (OR)

Range = 0.0–0.9

p-value 0.01

0.03 0.07

1.0 2.67

1.03–6.93

0.04

0.07 0.03

1.0 0.35

0.14–0.94

0.03

This study has shown that, for these intensive dairy goat operations in central Mexico, less sloped rump angles seems to favour reproduction, because animals with the highest pin bones had larger and heavier litters than goats with marked sloped rump angles. Consequently, selection based on rump angle should have an impact on prolificacy and birth litter weight. This study has shown that a relationship exists between strength of goats and litter size. In addition, stronger udder support lead to lower odds of non-infection abortion and occurrence of stillbirths, which suggest that some traits linked to high milk yield were antagonist to some reproductive traits. Acknowledgements The authors gratefully acknowledge The University of California Institute for Mexico and the United States (UC MEXUS) and CONACYT (Mexico) for generously providing a fellowship to carry out this study. The authors also thank Jose Oliveros Oliveros and Javier Morales for allowing access to data files.

References American Dairy Goat Association, 1993: Linear Appraisal System for Goats. American Dairy Goat Association, Spindale, NC. Amoah EA, Gelaye S, Guthrie P, Rexroad CE Jr, 1996: Breeding season and aspects of reproduction of female goats. J Anim Sci 74, 723–728. Astiz BS, Gonzalez MJV, Ayala GL, Monge VA, 2002: The Influence of the Pelvis Conformation on the Incidence of Uro-vagina. An Epidemiological Study. XXII World Buatrics Cong., Hannover, Germany, pp. 362–365. Bath GF, van Wyk GA, Pettey KP, 2005: Control measures for some important and unusual goat diseases in southern Africa. Small Rumin Res 60, 127–140. Berry DP, Buckley F, Dillon P, Evans RD, Veerkamp RF, 2004: Genetic relationships among linear type traits, milk yield, body weight, fertility and somatic cell count in primiparous dairy cattle. Irish J Agr Food Res 43, 161–176. Boelling D, Pollott GE, 1998: Locomotion, lameness, hoof and leg traits in cattle: II. Genetic relationships and breeding value. Livest Prod Sci 54, 205–215. Brotherstone S, 1994: Genetic and phenotypic correlations between linear type traits and production traits in HolsteinFriesian dairy cattle. Anim Prod 59, 183–187. Burguete I, Quiles A, Ramirez A, Hevia ML, Vallejo M, 1998: Effect of buck, year and season of insemination on prolificacy of Murciano–Granadina goats. Small Rumin Res 29, 121–123. Caraviello DZ, Weigel KA, Gianola D, 2004: Analysis of the relationship between type traits and functional survival in US Holstein cattle using a Weibull proportional hazards model. J Dairy Sci 87, 2677–2686.

 2008 The Authors. Journal compilation  2008 Blackwell Verlag

604

M Mellado, J Mellado, M Valencia and W Pittroff

Chawla DS, Bhatnagar DS, 1984: Reproductive performance of Alpine and Saanen does under intensive management. Indian J Anim Sci 54, 789–792. Constantinou A, 1989: Genetic and environmental relationships of body weight, milk yield and litter size in Damascus goats. Small Rumin Res 2, 163–174. Cue RI, Monardes HG, Hayes JF, 1990: Relationships of calving ease with type traits. J Dairy Sci 73, 3586–3590. Dadati E, Kennedy BW, Burside EB, 1986: Relationships between conformation and calving interval in Holstein cows. J Dairy Sci 69, 3112–3119. Engeland IV, Waldeland H, Andresen Ø, Løken T, Bjo¨rkman C, Inge jerka˚s I, 1998: Foetal loss in dairy goats: an epidemiological study in 22 herds. Small Rumin Res 30, 37–48. Eriksson S, Nasholm A, Johansson K, Philipsson J, 2004: Genetic parameters for calving difficulty, stillbirth, and birth weight for Hereford and Charolais at first and later parities. J Anim Sci 82, 375–383. Fahmy MH, 1990: Development of DLS breed of sheep: genetic and phenotypic parameters of date of lambing and litter size. Canadian J Anim Sci 70, 771–778. Fleiss JS, 1981: Statistical Methods for Rates and Proportions, 2nd ed. Wiley, New York, NY. Freetly HC, Leymaster KA, 2004: Relationship between litter birth weight and litter size in six breeds of sheep. J Anim Sci 82, 612–618. Garbarino EJ, Hernandez JA, Shearer JK, Risco CA, Thatcher WW, 2004: Effect of lameness on ovarian activity in postpartum Holstein cows. J Dairy Sci 87, 4123–4131. Haile-Mariam M, Bowman PJ, Goddard ME, 2004: Genetic parameters of fertility traits and their correlation with production, type, workability, liveweight, survival index and cell count. Aust J Agric Res 55, 77–87. Hall DG, Gilmour AR, Fogarty NM, 1994: Variation in reproduction and production of poll dorset ewes. Aust J Agric Res 45, 415–426. Hawk HW, 1987: Transport and fate of spermatozoa after insemination of cattle. J Dairy Sci 70, 1487–1503. Larroque H, Rupp R, Moureaux S, Boichard D, Ducrocq V, 1999: Genetic parameters for type and functional traits in the French Holstein breed. Intern workshop on EU concerted action of genetic improvement of functional traits in cattle (GIFT). Wageningen, the Netherlands. Interbull Bull 23, 169–179. Lucy MC, 2001: ADSA foundation scholar award. Reproductive loss in high-producing dairy cattle: where will it end? J Dairy Sci 84, 1277–1293. Luo MF, Wiggans GR, Hubbard SM, 1997: Variance component estimation and multitrait genetic evaluation for type traits of dairy goats. J Dairy Sci 80, 594–600. Meijering A, 1984: Dystocia and stillbirth in cattle-A review of causes, relations and implications. Livest Prod Sci 11, 143–177. Melendez P, Bartolome J, Archbald LF, Donovan A, 2003: The association between lameness, ovarian cyst and fertility in lactating dairy cows. Theriogenology 59, 927–937. Mellado M, Foote RH, Borrego E, 1991: Lactational performance, prolificacy and relationship to parity and body weight in crossbred native goats in northern Mexico. Small Rumin Res 6, 167–174. Mellado M, Valde´z R, Garcı´ a JE, Lo´pez R, Rodrı´ guez A, 2006: Factors affecting the reproductive performance of goats under intensive conditions in a hot arid environment. Small Rumin Res 63, 110–118. Mellado M, Olivares L, Pittroff W, Dı´ az H, Lo´pez R, Villarreal JA, 2007: Oral morphology and dietary choices of goats on rangeland. Small Rumin Res 71, 194–199.

Meyer CL, Berger PJ, Koehler KJ, 2000: Interactions among factors affecting stillbirths in holstein cattle in the United States. J Dairy Sci 83, 2657–2663. Norman HD, Powell RL, Wright JR, Cassell BG, 1988: Phenopypic and genetic relationship between linear functional type traits and milk yield for five breeds. J Dairy Sci 71, 1880–1896. NRC, 1981: Nutrient Requirements of Goats: Angora, Dairy, and Meat Goats in Temperate and Tropical Countries. National Academy Press, Washington, DC. Osuagwuh AIA, 1991: Influence of doe age on incidence of multiple births and perinatal reproductive wastage in West African Dwarf goats. J Agric Sci 117, 265–269. Perez-Cabal MA, Alenda R, 2002: Genetic relationships between lifetime profit and type traits in Spanish Holstein cows. J Dairy Sci 85, 3480–3491. Perez-Razo M, Sanchez F, Torres-Hernandez G, BecerrilPerez C, Gallegos-Sanchez J, Gonzalez-Cosıo F, MezaHerrera C, 2004: Risk factors associated with dairy goats stayability. Liv Prod Sci 89, 139–146. Peris S, Caja G, Such X, 1999: Relationships between udder and milking traits in Murciano-Granadina dairy goats. Small Rumin Res 33, 171–179. Pryce JE, Coffey MP, Brotherstone S, 2000: The genetic relationship between calving interval, body condition score and linear type and management traits in registered Holsteins. J Dairy Sci 83, 2664–2671. Rogers GW, McDaniel BT, 1989: The usefulness of selection for yield and functional type traits. J Dairy Sci 72, 187–192. Royal MD, Pryce JE, Woolliams JA, Flint APF, 2002: The genetic relationship between commencement of luteal activity and calving interval, body condition score, production, and linear type traits in Holstein-Friesian dairy cattle. J Dairy Sci 85, 3071–3080. SAS Institute, 2004: SAS User’s Guide. Statistics, Version 9.1. SAS Inst. Inc., Cary, NC. Schneider M, del P, Durr JW, Cue RI, Monardes HG, 2003: Impact of type traits on functional herd life of Quebec Holsteins assessed by survival analysis. J Dairy Sci 86, 4083–4089. Sewalem A, Kistemaker GJ, Miglior F, Van Doormaal BJ, 2004: Analysis for the relationship between survival in Canadian Holsteins using a Weibull proportional hazards model. J Dairy Sci 87, 3938–3946. Sewalem A, Kistemaker GJ, Van Doormaal BJ, 2005: Relationship between type traits and longevity in Canadian Jerseys and Ayrshires using a Weibull proportional hazards model. J Dairy Sci 88, 1552–1560. Shapiro LS, Swanson LV, 1991: Relationships among rump and rear leg type traits and reproductive performance in Holsteins. J Dairy Sci 74, 2767–2773. Smith MC, 1980: Caprine reproduction. In: Morrow DA (ed.), Current Therapy in Theriogenology. W.B. Saunders, Philadelphia, PA, pp. 971. Thomas CL, Vinson WE, Pearson RE, Dickinson FN, Johnson LP, 1984: Relationships between linear type scores, objective type measures, and indicators of mastitis. J Dairy Sci 67, 1281–1292. Van Eerdenburg FJCM, Karthaus D, Taverne MAM, Merics I, Szenci I, 2002: The relationship between estrous behavioral score and time of ovulation in dairy cattle. J Dairy Sci 85, 1150–1156. Vollema AR, Groen AF, 1997: Genetic correlations between longevity and conformation traits in an upgrading dairy cattle population. J Dairy Sci 80, 3006–3014. Waldron DF, Thomas DL, 1992: Increased litter size in Rambouillet sheep: II. Expected response from alternative selection criteria. J Anim Sci 70, 3345–3350.

 2008 The Authors. Journal compilation  2008 Blackwell Verlag

Linear Type Traits and Fertility in Goats Wall E, White IMS, Coffey MP, Brotherstone S, 2005: The relationship between fertility, rump angle, and selected type information in Holstein-Friesian cows. J Dairy Sci 88, 1521–1528. Wiggans GR, Hubbard SM, 2001: Genetic evaluation of yield and type traits of dairy goats in the United States. J Dairy Sci 84, E69–E73.

605 Submitted: 27 Jul 2007 Author’s address (for correspondence): Miguel Mellado, UAAAN, Dept. Nutricio´n y Alimentos, Saltillo, Coah 25315, Me´xico. E-mail: [email protected]

 2008 The Authors. Journal compilation  2008 Blackwell Verlag