Abstract
The objective of this study was to evaluate whether pre-weaning heifer calves divergent for residual feed intake (RFI) or residual feed intake and body weight gain (RIG) exhibit differences in thermography, blood, and ruminal parameters. Thirty-two Gyr heifer calves were enrolled in a 63-d trial and classified into 2 feed efficiency (FE) groups based on RFI and RIG (mean ± 0.5 SD). The groups were classified as high efficiency (HE) RFI (HE RFI, n = 9), HE RIG (HE RIG, n = 10), low efficiency (LE) RFI (LE RFI, n = 10), and LE RIG (LE RIG, n = 11). The amount of whole milk provided for each calf was calculated based on their metabolic weight at birth (42% x BW0.75). The liquid diet was divided into two meals at 0700 and 1400 h. The total solid diet (TSD) was composed of 92% concentrate and 8% of Tifton 85 hay chopped in 5-cm lengths, as fed. Intake was measured daily. Blood concentrations of insulin, beta hydroxybutyrate, urea, and glucose, and ruminal pH, N-NH3, and volatile fatty acids (VFA) were evaluated at 14, 28, 42, 56, and 70 days of age. Thermal images of the calves were taken with an infrared camera (FLIR T420, FLIR Systems Inc., Wilsonville, OR) on d 56 (±3) at 0600 h, before the morning feeding. Total VFA concentration and propionate as % of total VFA were 24.2% and 22.2% lower in HE RFI compared to LE RFI calves, respectively. On the other hand, acetate as % of total VFA was 10.6% greater in HE RFI than LE RFI calves. Blood urea concentration tended to be greater in LE RFI than HE RFI calves. High efficiency HE RIG tended to have 6.8% greater acetate and 15.4% lower propionate as % of total VFA than LE RIG. Blood insulin concentration was greater and blood glucose tended to be greater for LE RIG than HE RIG group. Low efficiency RIG group had greater left rib, left flank, and anus surface temperature measured by infrared thermography than the HE RIG group. Differences in ruminal fermentation do not seem to be associated with pre-weaning calves efficiency, while differences in protein metabolism seem to affect RFI during this phase. Infrared thermography appears to be correlated to RIG in pre-weaning heifer calves.
Highlights
In milk production systems, feed corresponds to 50% of the total cost of production [1]; improving feed efficiency (FE) is essential to increasing profitability [2]
The objective of the present study was to evaluate whether pre-weaning calves divergent for FE indexes (RFI and residual intake and body weight gain (RIG)) exhibit differences in thermography, blood, and ruminal parameters
Clear evidence of differences in these parameters when using residual feed intake (RFI) or RIG as indexes for calves was observed for proportions of acetate and propionate in rumen volatile fatty acids (VFA), blood glucose, insulin and urea depending on the FE index evaluated
Summary
In milk production systems, feed corresponds to 50% of the total cost of production [1]; improving feed efficiency (FE) is essential to increasing profitability [2]. As a tool to select more efficient animals, have been studied [3]. Residual feed intake (RFI) is a FE index calculated as the difference between actual and expected animal feed intake, at a certain level of production [4]. The independence of RFI from productive parameters led researchers to suggest that this measurement describes the inherent variation of basic metabolic processes, mainly related to intake and digestion, anabolism and catabolism, activity, and thermoregulation processes [5]. Development of potential physiological markers of feed efficiency can reduce the cost of identification and selection of efficient cows in future studies [6]
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