THE EFFECT OF DIETARY ENERGY SOURCE ON METABOLISM AND MILK PRODUCTION OF COWS.

In two previous reports I discussed the possibility of using more fibrous concentrates to supplement cows on pasture. More fibrous concentrates may have less negative influence on rumen pH, improved pasture dry matter (DM) intake and may be less expensive. To some extent those reports confirmed this expected outcome. On the other extreme it may be necessary to increase energy levels in the supplement which can be done by high starch or high fat or a combination of starch and fat. The question is how does this affect the metabolism of the cow and the resulting milk yield and milk components.

The objective of the study referenced below was in line with this perspective. The authors evaluated the effect of different levels and types of energy sources on the energy balance and milk production of dairy cows. Holstein cows from the Elsenburg herd were used in the study. During the dry period, pregnant heifers and cows were maintained under similar conditions. Following parturition, cows grazed cultivated, irrigated kikuyu-ryegrass pastures for 154 days. These cows were divided into three groups according to lactation number, body weight and milk yield in the previous lactation. Groups of cows were allocated randomly to three treatments consisting of different concentrates supplemented to the trial cows. The main energy sources of the supplements were provided by starch and/or fat. Treatments were: (1) a standard commercial concentrate as Control treatment, (2) a high glucose-providing concentrate containing high starch-low fat levels using maize as energy source (Treatment 1) and (3) a combination of the glucose-providing concentrate offered for the first 60 days of the lactation as per Treatment 1, with a high fat-providing concentrate from 61 days, using wheat bran and calcium salts of palm fatty acids as energy sources (Treatment 2). Cows were milked twice a day and concentrate supplements were fed after each milking.

 The results show no differences in non-esterified fatty acids (NEFA), β-hydroxybutyrate (BHB) and plasma urea during the period before calving. After calving NEFA and BHB were similar among treatments for multi-lactation cows but levels were affected by diet for first-calf heifers (these metabolites were higher in Control compared to treatments, suggesting somewhat underfed in Control). Plasma urea was also affected by diet, with levels being lower for Control in both first-calf heifers and multi-lactation cows. The milk yields were higher for Treatments 1 and 2 compared to Control for both first-calf heifers and multi-lactation cows. In addition, the milk components were affected by Treatments 1 and 2; high lactose and protein for first-calf heifers and high lactose for multi-lactation cows. This suggests that dietary energy supplements of this nature can affect metabolic adaptations in the liver to drastically change energy requirements while supporting high milk yields.  

Reference:

B.A. Useni, C.J.C. Muller & C.W Cruywagen, 2015. Effect of energy sources on energy partition and milk production of dairy cows. Proc. of the 48^th SASAS Congress, 21-23 September, Empangeni.