Assesment of the dietary level of minerals for lactation in crossbred cows in Kerala under different feeding systems

Abstract

An investigation spread over a period of eight months was undertaken in crossbred dairy cattle to assess the dietary levels of minerals for lactation under different feeding systems. Twelve healthy crossbred cows at eight months pregnancy having an average peak yield of minimum eight litres per day in their previous lactation were divided into two groups of six each as uniformly as possible with regard to age and milk yield and were allotted to two dietary treatments viz. ration A consisting of basal concentrate mixture and green grass as roughage (Grass based diet) and ration B consisting of basal concentrate mixture and paddy straw as roughage (Straw based diet). All the experimental animals were fed as per NRC (1989) standards and maintained individually on their respective dietary regime from two months before calving to six months of lactation. Average dry matter intake, milk yield, milk fat percentage, serum minerals, mineral content of milk, digestibility of nutrients, N balance, balance of Ca, P, Mg, Cu and Zn, incidence of metabolic disorders and reproductive performance were the criteria employed for evaluation. Average body weights of animals revealed no significant difference for both the groups during all the fortnights studied. Significant increase (P<0.01) in the average dry matter intake was observed for the animals of group I compared to group II and the highest dry matter intake was observed during the eighth and third fortnight, respectively. Average daily milk yield and fat per cent in milk in all the twelve fortnights did not differ significantly between the groups. The average haemoglobin and mineral concentration in serum and milk at the first, third and sixth month of lactation for the animals in group I and II did not differ significantly. The mineral content in serum and milk in both groups were within the normal range reported for the species. The average digestibility coefficients of dry matter, nitrogen free extract, neutral detergent fibre and acid detergent fibre in group I and II differed significantly (P<0.01) with higher values observed for animals of group I fed grass based diet. No significant difference could be observed in the digestibility coefficient of crude protein and ether extract between the group I and II during the third and sixth month of lactation. The average digestibility coefficients of crude fibre for the third month of lactation between the group I and II did not differ significantly but those for the sixth month of lactation differed significantly (P<0.01) with higher values for group I animals fed grass based diet. Results with respect to balance of N, Ca, P and Mg did not differ significantly (P>0.05) between the two groups for both periods of lactation whereas that for Cu during the third month and that for Zn during both periods of lactation differed significantly (P<0.01) with higher balance for the group I fed grass based ration. There was no incidence of metabolic disorders like hypocalcaemia, hypomagnesaemia and ketosis in both groups of animals. The reproductive performances of animals of both groups were almost similar. An overall critical evaluation of the results obtained in the present study helps to infer that grass based feeding system had a significant effect on improving the digestibility of dry matter, crude fibre, nitrogen free extract, NDF, ADF and the bioavailability of Cu and Zn. Positive balance was obtained for the minerals studied along with their normal content in serum and milk and the animals were apparently healthy without any incidence of metabolic disorders or deficiency symptoms. Hence it is inferred that NRC (1989) requirements of Ca, P, Mg, Cu and Zn is applicable to crossbred lactating cattle of Kerala under both grass and straw based system. The study also indicates that the requirements of P, Mg, Cu and Zn can be solely met from their content in the feed ingredients and Ca is the only element that needs to be supplemented under both feeding system.