Effect of dietary fat supplementation on food digestion and milk protein production by lactating cows and goats

Abstract

Concentrations of nutrients needed in the rations of high producing dairy cows are determined by the animals’ requirements and by their potential feed intake. As the genetic potential for milk production increases, it is more difficult to formulate rations with the required concentrations of energy. Energy density of rations can be increased by replacing forage with grains, however, this can lead to a multitude of digestive and metabolic problems like acidosis, rumen indigestion, bloat, reduced fibre digestibility, secretion of milk with low concentrations of fat, lameness and liver damage. Substitution of fat for a grain is a method of increasing energy density as fats have more than twice the energy density of grain. But, the main problem in using fats in dairy diets is that it depresses milk protein content which is important for the consumer and cheese manufacturers. This project was designed to further investigate the effects of fat supplementation of diets on diet digestibility and milk composition with a particular focus on milk protein content. The studies conducted were: 1. The effects of oilseed (whole cottonseed) supplementation on rumen function and microbial synthesis in sheep. 2. The effect of supplementing diets with soybean oil and different carbohydrate sources with different degrees of rumen solubility on milk production and composition in dairy cows. 3. The effect of post-ruminal infusion of soybean oil on food intake, milk production and composition of goats. 4. The effect of post-ruminal infusion of sodium caseinate and the amino acids lysine and methionine on milk production and milk composition of goats supplemented with soybean oil. In the first experiment seven sheep were fed three diets. The control diet had a roughage to concentrate ratio of 1:1. The other two had 15% and 30% of the concentrate energy replaced with whole cottonseed. The double marker method (Cr-EDTA and ytterbium chloride) was used to estimate flow rate of nutrients from rumen and S35 was used to estimate microbial synthesis. Despite repeating this experiment, the results obtained using the double marker technique were not satisfactory. Consequently, the flow rate of nutrients was calculated using a single marker (Cr-EDTA). No significant differences were found for extent of nutrient digestibility in the rumen or flow of nutrients from the rumen. However, there were significant differences for DM and NDF digestibilities in the total tract. The results of the study with dairy cows indicated that oil can replace or be fed with carbohydrate sources (grain or molasses) without any significant effect on milk production or composition. A combined supplement of sorghum, soybean oil and formaldhayde treated soybean meal gave the best performance by grazing dairy cows in mid lactation.