Abstract
Abstract. Forty Holstein dairy cows in their first and second lactation were used in a lactation study from 4-week prepartum through 14-week postpartum to investigate the potential effect of feeding different levels of ruminally protected methionine and choline on milk yield persistency of Holstein dairy cows. Cows were randomly assigned to receive one of the following treatments: 18 g/d of rumen-protected methionine (RPM), 60 g/d of rumenprotected choline (RPC), 18 g/d of RPM + 60 g/d of RPC, or neither supplement (control). The use of polynomial equations revealed that the polynomial coefficients of regression were closer (P<0.05) to zero for RPM+RPC-fed cows than for other cows. Therefore, RPM+RPC-fed cows had a more persistent (P<0.05) early-lactation milk yield than did other cows. Cows fed RPM+RPC had the lowest health problems compared with other groups. The treatments significantly affected actual milk yield (P<0.05), 4 % fat-corrected milk (FCM) (P<0.01) and energy-corrected milk (ECM) (P<0.01) across lactation weeks. The treatments significantly affected average dry matter intake (DMI) for the first 14 week postpartum (P<0.05). Also, treatments significantly affected lactose percentage of milk across lactation weeks (P<0.01). In general, it was expected that RPM+RPC-fed cows with greater persistency of lactation would be healthier because the incidence of metabolic and reproductive disorders and negative energy balance that originate from the physiological stress of high milk yield would be lower.
Highlights
Persistency of lactation can be defined as the ability of a cow to maintain milk production after peak yield, with cows being persistent if they tend to maintain their peak yield within a lactation period (SWALVE 1995, BAFFOUR-AWUAH et al 1996, TAKMA and AKBAS 2007)
The Neutral detergent fibre (NDF) was assayed with a heat-stable amylase and both NDF and acid detergent fibre (ADF) are expressed inclusive of residual ash
The simultaneous significant effects of rumen-protected methionine (RPM) and rumenprotected choline (RPC) on the curvature of lactation arch were confirmed by the variance analysis of the polynomial coefficients (Table 3)
Summary
Persistency of lactation can be defined as the ability of a cow to maintain milk production after peak yield, with cows being persistent if they tend to maintain their peak yield within a lactation period (SWALVE 1995, BAFFOUR-AWUAH et al 1996, TAKMA and AKBAS 2007). The objective of present study was to investigate the potential effects of supplementing ruminally protected forms of methionine and choline to the diets of Holstein dairy cows on milk yield persistency and production performance in the first 14 weeks of lactation. The use of polynomial equations to regress the actual milk yield of individual cows against lactation weeks revealed that linear, quadratic and cubic coefficients of regression were closer (P
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