J. Dairy Sci. 96:7818–7829 http://dx.doi.org/10.3168/jds.2013-6981 © American Dairy Science Association®, 2013.
Carbohydrate supplements and their effects on pasture dry matter intake, feeding behavior, and blood factors associated with intake regulation A. J. Sheahan,1 J. K. Kay, and J. R. Roche
DairyNZ, Private Bag 3221, Hamilton, 3240, New Zealand
ABSTRACT
Supplementary feeds are offered to grazing dairy cows to increase dry matter (DM) and metabolizable energy (ME) intakes; however, offering feed supplements reduces pasture DM intake, a phenomenon known as substitution. The objective of the study was to investigate changes in blood factors associated with intake regulation in monogastric species in pasture-fed dairy cows supplemented with either a starch- or nonforage fiber-based concentrate. Fifteen multiparous Friesian × Jersey cross cows were assigned to 1 of 3 treatments at calving. Measurements were undertaken in wk 8 of lactation. Treatments were pasture only, pasture plus a starch-based concentrate (3.5 kg of DM/cow per day; STA), and pasture plus a nonforage fiber-based concentrate (4.4 kg of DM/cow per day). Pelleted concentrates were fed at an isoenergetic rate in 2 equal portions at a.m. and p.m. milkings. Measurements were undertaken to investigate differences in pasture DM intake, feeding behavior, and profiles of blood factors for 4 h after a.m. and p.m. milkings, the periods of intensive feeding in grazing cows. Supplementing cows with STA concentrate reduced pasture DM intake to a greater extent than the fiber concentrate, although time spent eating did not differ between treatments. The blood factor response to feeding differed between the a.m. and p.m. feeding events. Blood factors associated with a preprandial or fasted state were elevated prefeeding in the a.m. and declined following feeding, whereas satiety factors increased. In comparison, the blood factor response to feeding in the p.m. differed, with responses to feeding delayed for most factors. Plasma ghrelin concentration increased during the p.m. feeding event, despite the consumption of feed and the positive energy state remaining from the previous a.m. feeding, indicating that environmental factors (e.g., sunset) supersede physiological cues in regulating feeding behavior. The greater reduction in pasture DM intake for the STA treatment in the p.m. may be related to the level of
Received May 1, 2013. Accepted August 8, 2013. 1 Corresponding author:
[email protected]
hunger or satiety before the feeding event and not solely to the consumption of supplement. Data indicate that neuroendocrine factors are, at least in part, responsible for the substitution of pasture for supplementary feeds. Key words: dairy cow, supplementary feeding, blood factor INTRODUCTION
Low DMI is a major limitation to productivity in pasture-based systems (Kolver and Muller, 1998). Supplementary feeds are offered to grazing cows to increase DM and ME intakes; however, offering feed supplements reduces pasture DMI (Stockdale, 2000; Bargo et al., 2003; Sheahan et al., 2011). This is known as substitution, with the pasture refused relative to supplement fed referred to as substitution rate (SR); SR is reflected in a reduction in grazing time (McGilloway and Mayne, 1996). Bargo et al. (2003) and Sheahan et al. (2011) reported a 12 min decrease in grazing time for every 1 kg of concentrate supplement DM consumed. However, SR is not fixed; Stockdale (2000) reported that SR was 8 to 10% greater with forage supplements compared with concentrate feeds, whereas Stakelum and Dillon (1988) and Meijs (1986) reported greater pasture DMI when cows were supplemented with a nonforage fiber (NFF)-based supplement compared with an equivalent amount of energy from a starchbased supplement. These studies indicate an effect of feed composition on SR and, in particular, an effect on intake regulation. In evaluating the primary neuroendocrine factors implicated in intake regulation in monogastric species (Arora and Anubhuti, 2006), Roche et al. (2008) reported that these factors were also likely regulatory factors in ruminant DMI. Consistent with this, Roche et al. (2007) reported a linear decline in plasma ghrelin 2 h after supplement feeding in grazing cows, providing for the first time, a neuroendocrine basis for SR in grazing cows. Gibb et al. (1998), Taweel et al. (2004) and Sheahan et al. (2011, 2013a) reported that the major grazing bouts occurred immediately after sunrise and before sunset and that the grazing bout before sunset was the most intensive. However, grazing
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SUPPLEMENT TYPE EFFECTS IN PASTURE-FED COWS
behavior data indicate that different factors potentially regulate DMI during the post-sunrise and pre-sunset grazing bouts. Consistent with this, Sheahan et al. (2013a) reported distinct differences in the temporal profile of blood factors implicated in intake regulation during the post-sunrise and pre-sunset grazing bouts. Although Sheahan et al. (2013a) identified candidate metabolites and hormones that could plausibly have an intake regulatory role in dairy cows, the blood sampling was not sufficiently frequent (every 4 h) to determine associations with certainty. Accordingly, the objective of this study was to determine if changes in feeding behavior coincided with changes in blood factors, using an intensive blood sampling regimen that coincided with the major feeding bouts after sunrise and before sunset. In addition, the effects of supplement type on feeding behavior, pasture DMI, and the profile of blood factors were investigated. MATERIALS AND METHODS
This experiment was conducted at Lye Farm (DairyNZ, Hamilton, New Zealand) on August 24 to 26, 2010, and all procedures were approved by the Ruakura Animal Ethics Committee, Hamilton, New Zealand. Experimental Design
The 15 multiparous Friesian × Jersey cross dairy cows used for this study were part of a larger experiment (Higgs et al., 2013) and had been assigned to 1 of 3 treatments at calving. Treatments were balanced for milk production (mean of the first 100 DIM from the previous lactation for multiparous cows; 17.7 ± 0.7 kg of milk/cow per day; mean ± SD), precalving BW (549 ± 29 kg), BCS (4.5 ± 0.3; 10-point scale; Roche et al., 2004), and age (4.5 ± 0.2 yr). Treatments were pasture only (PAS), pasture plus a starch-based concentrate (3.5 kg of DM/cow per day; STA), and pasture plus a nonforage fiber-based concentrate (4.4 kg of DM/cow per day; FBR). Cows had been on treatment for 8 wk (56 DIM), with an average milk production of 23.1, 27.7, and 26.2 (SE of the difference: 1.34) kg/d for the PAS, STA, and FBR groups, respectively (Higgs et al., 2013), when this experiment commenced. Pelleted concentrates were formulated using the Cornell Net Carbohydrate and Protein System version 6.1 (Tylutki et al., 2008; Van Amburgh et al., 2010) and fed at an isoenergetic rate in 2 equal portions at a.m. and p.m. milkings to supply sufficient ME and MP daily to support 30 kg of potential milk production (assuming 13 kg of pasture DMI; 11 MJ of ME/kg of DM; Higgs et al., 2013).
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Feed Management
The current experiment required serial blood sampling every 10 min for 240 min. A major restriction to achieving this in grazing dairy cows is the logistics of taking frequent blood samples without disrupting normal grazing behavior. As the majority of grazing activity occurs in the 3 to 4 h after a.m. and p.m. milking (Sheahan et al., 2011, 2013a), cows were offered their usual concentrate allocation and pasture allowance while tethered in a tie-stall facility immediately after milking. Cows had been previously trained to use the facility during the 2 wk leading up to the experimental measurement periods to ensure normal feeding behavior was maintained. This was achieved by regularly tethering animals in the facility after a.m. and p.m. milkings for up to 4 h, with access to freshly cut pasture. The sampling was conducted over 2 d, so that cows could exhibit normal grazing behavior before each 240min measurement period, with sampling on d 1 following a.m. milking and sampling on d 2 following p.m. milking. Throughout the larger experiment (Higgs et al., 2013), cows were offered supplements during a.m. and p.m. milkings; however, on d 1 of sampling, cows were milked in the a.m. and offered supplements in the tie-stall facilities immediately following milking. Pasture was not offered until cows receiving supplement had consumed their respective supplement, which took less than 4 min. Blood samples were collected at 0 min (i.e., before supplements were offered) and every 10 min after pasture was offered to all 15 animals for a period of 240 min, after which cows were returned to the paddock. On d 2, cows were milked in the a.m. as normal and returned to the paddock; after the p.m. milking, the feeding and blood sampling protocol described for d 1 were repeated. Pasture and Animal Measurements
Pasture and Supplement Intakes and Feeding Behavior. Preweighed freshly cut pasture was offered ad libitum to all cows individually once supplements had been consumed, which occurred within 4 min. After 240 min, pasture orts were weighed and recorded. The difference between offered and orts was recorded as pasture intake. Representative samples of each supplement and pasture offered were collected for DM and feed quality analysis. Samples were dried at 100°C for 24 h for DM analysis and 60°C for 72 h for quality and nutrient composition; dried samples were ground to pass through a 1.0-mm sieve (Christy and Norris Laboratory Mill; Christy Turner Ltd., Suffolk, UK) and analyzed by wet chemistry for the nutrients required Journal of Dairy Science Vol. 96 No. 12, 2013
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Table 1. Chemical composition of pasture samples fed during the a.m. and p.m. measurement periods and the starch- and fiber-based concentrate supplement fed in equal portions at a.m. and p.m. milkings Item DM (%) % of DM CP ADF NDF Lignin NFC Starch Fat Ash IVTD, 24 h2 (% of DM) NDFD, 24 h3 (% of NDF) ME4 (MJ/kg of DM)
Pasture
Starch1
Fiber1
18.3
96
96.1
28.5 21.4 36.7 2.1 28.9 0.5 5.3 9.83 92 78 14.1
9.4 5.5 14.5 2.1 71.1 59.5 3.7 2.25 94 58 14.5
17.8 12.5 34.5 3.5 37.9 21.7 7.3 4.66 78 35 11.71
1 Starch and fiber pelleted concentrates formulated using the Cornell Net Carbohydrate and Protein System (CNCPS) version 6 (Tylutki et al., 2008; Van Amburgh et al., 2010). 2 IVTD = in vitro true digestibility. 3 NDFD = NDF digestibility. 4 Metabolizable energy calculated from IVTD: (IVTD × 0.172 − 1.707) (CSIRO, 2007).
for diet simulation in the Cornell Net Carbohydrate and Protein System (Dairy One, Ithaca, NY; Table 1). Feeding behavior was visually assessed every 10 min for 240 min for every cow during both a.m. and p.m. measurement periods, with eating, ruminating or idle recorded. It was accepted that cows were in observed behavior for the 10 min between recordings (Gary et al., 1970). Total time spent on each behavior was then calculated for each cow during both the a.m. and p.m. measurement periods, and analyzed as described in the Statistical Analysis section. Jugular Catheter and Blood Sampling. On the day before the a.m. intensive bleeding regimen, a catheter (14 gauge × 19.6 cm; DelMed Inc., New Brunswick, NJ) was inserted into the jugular vein of each cow under local anesthesia. After each blood collection, catheters were flushed with 10 mL of isotonic saline containing 50 IU/mL of sodium heparin (Multiparin; Fisons Pharmaceuticals, NSW, Australia). Blood samples were collected into evacuated 10-mL tubes containing 15% K3 EDTA, immediately placed on ice, and centrifuged at 1,500 × g for 12 min at 4°C within 30 min of collection. Plasma samples were aliquoted in duplicate; one of these aliquots was acidified using 0.1 N HCl and treated with phenylmethylsufonyl fluoride for ghrelin analysis (as per kit instructions). Both aliquots of plasma were stored at −20°C until further analysis. Plasma Hormone and Metabolite Assays. Plasma glucose, NEFA, and BHBA were measured using a Hitachi 717 analyzer (Roche, Basel, Switzerland) at 30°C by Gribbles Ltd. (Hamilton, NZ). The Journal of Dairy Science Vol. 96 No. 12, 2013
intra- and interassay coefficient of variation for both assays was
