Abstract
This study aimed to estimate energy requirements of pregnant Holstein × Gyr cows. Different planes of nutrition were established by two feeding regimens: ad libitum or maintenance. Sixty-two nonlactating cows with average body weight of 480 ± 10.1 kg and an age of 5 ± 0.5 years were used. Cows were divided into three groups: pregnant (n = 44), non-pregnant (n = 12), and baseline reference (n = 6). The 56 pregnant and non-pregnant cows were randomly allocated into a feeding regimen: ad libitum or maintenance. To evaluate the effects of days of pregnancy, pregnant and non-pregnant animals were slaughtered at 140, 200, 240, and 270 days of pregnancy. Energy requirements for maintenance differed between pregnant and non-pregnant cows, thus two equations were developed. Net energy and metabolizable energy requirements for maintenance of non-pregnant cows were 82 kcal/kg empty body weight0.75/day and 132 kcal/kg empty body weight0.75/day, respectively. The efficiency of use of metabolizable energy for maintenance of non-pregnant cows was 62.4%. Net energy and metabolizable energy for maintenance of pregnant cows were 86 kcal/kg empty body weight0.75/day and 137 kcal/kg empty body weight0.75/day, respectively. Efficiency of use of metabolizable energy for maintenance of pregnant cows was 62.5%. The efficiency of use of metabolizable energy for gain was 41.9%. The efficiency of use of metabolizable energy for pregnancy was 14.1%. Furthermore, net energy requirement for pregnancy was different from zero from day 70 of pregnancy onwards. In conclusion, net energy and metabolizable energy requirements for maintenance of non-pregnant cows are different from pregnant cows. Furthermore, we believe that the proposed non-linear equations to estimate net energy requirements for pregnancy are more adequate than current NRC equation, and should be recommended for Holstein × Gyr cows.
Highlights
In dairy cattle, the late pregnancy period is important to prepare the mammary gland for lactation
Where: heat production and metabolizable energy intake are in Mcal/kg empty body weight0.75/day
The net energy requirement for maintenance (NEm) requirement for pregnant cows was 86 kcal/kg empty body weight0.75/day or 80 kcal/kg body weight0.75/day. This value, with approximations, is equal to the NEm suggested by the NRC [6]
Summary
The late pregnancy period is important to prepare the mammary gland for lactation. Energy requirements for pregnancy in the NRC [6] were established according to results obtained by Bell et al [3] and the efficiency of use of metabolizable energy by the conceptus was estimated by Ferrell et al [1]. According to Bell et al [3], the energy required for pregnancy is significant from 190 days, with linear accretion until 279 days. These pregnancy requirements were obtained with cows from Bos taurus breeds. When evaluating requirements for animals from different breeds, such as crossbred Bos taurus × Bos indicus (Holstein × Gyr), there is no clear evidence that energy requirements for pregnancy would be the same
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