Influence of Cow Size and Breed Type on Energy Requirements2

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Abstract
Two studies were conducted to determine how cow size and breed type affect TDN requirements during the last trimester of gestation and to evaluate the effects of milk production potential on TDN needs. Cows studied were Hereford (HH), Angus × Hereford (AH), Charolais × Hereford (CH) and Brown Swiss × Hereford (SH). Weight loss was about 13 kg/cow during the last trimester of gestation in trial 1, with HH, AH, CH and SH cows consuming 4.0, 4.4, 4.2 and 4.7 kg of TDN/head/ day, respectively. When HH cows were used as a standard for comparison, TDN ratios during gestation were 100, 109, 106 and 118 for HH, AH, CH and SH cows, respectively. During calving season and first 2 months of lactation, weight loss was about 30 kg for HH, AH, CH and SH cows. Average TDN consumption during lactation was 5.0, 5.6, 5.6 and 6.6 kg/ head with TDN ratios of 100, 112, 112 and 132 for HH, AH, CH and SH cows, respectively. In trial 2, cow condition was equalized to near moderate condition in the last trimester of gestation by the feeding of an average of 2.9, 3.0, 3.2 and 3.9 kg of TDN/head/day to HH, AH, CH and SH cows, respectively. TDN needs during gestation were 2, 9 and 32% greater for AH, CH and SH cows, respectively, than for HH cows. Condition was maintained at near moderate among all breed groups from approximately 25 days before calving until cows went to spring pasture (96 days). Cows were fed an average of 4.7, 5.4, 5.4 and 6.6 kg TDN/day with TDN ratios of 100, 113, 114 and 139 for the HH, AH, CH and SH groups, respectively. These data suggest that weight alone cannot be used to accurately determine the energy requirements of the larger breeds or breeds with higher milk production potential. Multiple linear regression analysis was conducted to estimate relative TDN needs (kilogram/day) of cows during gestation (TDNG) and lactation (TDNL). The following prediction equations were used: TDNG2 = 3.79 + .0004 (W-547.22) − 1.6508 (C-3.21) and TDNL3 = 5.56 + .0053 (W-528.12) − .6819 (C-2.91) + .3584 (M-5.78), where W is individual cow weight (kilograms), C is condition score (1 = very thin, 3 = moderate condition, 5 = very fat) and M is estimated daily milk production (kilograms). Visual body condition score, combined with weight, appeared to predict relative TDN requirements of pregnant cows during late gestation more accurately than did weight alone. Similarly, condition score, when used with weight and estimated milk production, appeared to predict relative TDN needs more accurately during early lactation than did weight and milk production alone. Copyright © 1980. American Society of Animal Science . Copyright 1980 by American Society of Animal Science