Abstract
The aim of the present study was to examine the effect of nutrition on the pregnancy rate in Japanese Black cows. The experiments were carried out during two periods. In Period I, 61 dry cows were self-fed roughage, which was composed of two types of silage and hay, and adjusted to have a TDN sufficiency ratio of over 130% and a DMI sufficiency ratio of over 100%. In Period II, 29 dry cows were used, and according to the result of MPT in Period I, shelled corn was added to the roughage to yield a TDN sufficiency ratio of over 120 %, a DCP sufficiency ratio of less than 200 % and a DMI sufficiency ratio of over 100% . In both periods, feeds were analyzed for composition at every harvest and mixed using a TMR mixer. The amount of feed was adjusted to satisfy the requirements so that the body weight could be maintained from two months before embryo transfer (ET). Fresh and frozen embryos were used for ET. MPT was conducted on randomly selected cows one month after ET. The mean TDN sufficiency ratios were significantly different between PeriodsⅠandⅡ (p<0.01; 137% vs. 113 %). The mean DCP sufficiency ratios were also significantly different between PeriodsⅠandⅡ(p<0.01; 310% vs. 147%), as the protein content was reduced in PeriodⅡ. The DMI sufficiency ratios in Periods I and II were 106 and 114%, respectively. The mean NFC concentration was significantly different between PeriodsⅠandⅡ (p<0.01; 7.9% vs. 17.6%). Serum FFA, BHB and UN were significantly different between PeriodsⅠandⅡ (BHB: 419.6 vs. 296.1μmol/ℓ, p<0.01; BUN: 14.6 vs. 10.3 mg/dℓ, p<0.01; FFA: 68.2 vs. 43.0μEq/ℓ, p<0.05). These results indicate that the feed in Period I contained little NFC and a high level of DCP and therefore these cows had insufficient energy due to poor fermentation in the rumen. The total pregnancy rates after ET were significantly different between Periods ⅠandⅡ [p<0.05; 37.7% (23/61) vs. 65.5% (19/29)]. These results suggest that MPT was effective for feeding management to improve the pregnancy rate, and the pregnancy rates was negatively affected by imbalance of NFC and DCP, or excessive intake of DCP, in Japanese Black cows. In addition, it was found that feeding of too much forage grasses could cause excessive intake of CP.
