Study On The Requirement Of Dietary Metabolizable Glucose And Metabolizable Protein For 8 To 10-month-old Holstein Heifers

The ultimate goal of dairy farm is to produce the best cows from replacement heifers, so heifers’ rearing is a critical aspect in the dairy farm. Nutritional factors are still the important factors that affect the growth and development of the heifers. Proper assessment and evaluation of the feeding and management programmes of replacement heifers is required in dairy farm. The aim of this study was to determine the optimal dietary requirement of the metabolizable protein (MP) and metabolizable glucose (MG) and provide scientific guidance for rearing of heifers.In experiment 1, three dairy cattles with cannula were used to detect the MP content of ruminant common ingredients by the method of Nylon Bag. The MP content of ground corn grain, wheat bran, soybean meal, distillers dried grains with soluble(DDGS), wildrye grass hay, corn silage is 11.63%,9.33%,21.39%,20.52%,8.15% and 7.01% accordingly.In experiment 2, twenty-four Chinese Holstein heifers with similar age and weight were divided into four groups randomly. Heifers were fed on four different diets in which the MP content was 9.03%,9.55%,10.09% and 10.57% accordingly. The experimental period was 60 days. The results observed as follows:The ADG of heifers increased first, then dropped with the increase of the dietary MP content. When the MP content was 10.09%, the ADG of heifers reached the maximum of 1.09kg/d; when the MP content was 10.09%, the development of the body height, body length and the abdominal girth was better than other groups’; The total amount of volatile fatty acid (VFA) in rumen of heifers increased with the increase of dietary MP content (P<0.01); The apparent digestibility of nutrients was stable. There was no significant digestibility in four groups. It is concluded that the optimal dietary MP content was 10.09% for 8 to 10-month-old Holstein heifers.In experiment 3, twenty-four Chinese Holstein heifers with similar age and weight were divided into four groups randomly. Heifers were fed on four different diets in which MG/MP was 0.97,1.07,1.13 and 1.28 accordingly. The experimental period was 60 days. The results observed as follows:When the dietary MG/MP was 1.13, the ADG of heifers reached the maximum of 1.06kg/d. There was significant difference in four groups(P<0.05); When the dietary MG/MP was 1.13, the blood urea nitrogen(BUN) was significantly lower than other groups’(P<0.05); When the dietary MG/MP was 1.13, the energy and nitrogen was released synchronously in rumen; Higher dietary MG/MP can increased the number of protein-degrading bacteria and fiber-degrading bacteria; When the dietary MG/MP was 1.13, the body condition scores were better than other groups’. It is concluded that the optimal dietary MG/MP was 1.13 for 8 to 10-month-old Holstein heifers.