عنوان مقاله [English]
Introduction Dry period is an important factor for milk yield, udder health and also cows' reproduction. Persistency of milk production in high producing dairy cows, increased income from milk production per cow in 305 days. In the other side, in recent decades, much attention to increasing milk production in dairy cows and genetic selection of high producing animals, has been caused many problems such as negative energy balance and reproductive disorders. Shortening or removing the dry period, may to improve health status and reproductive performance of cows. The relationship between energy balance and reproduction is well proven. Body condition score (BCS) at mating, and duration and severity of negative energy balance after calving affect pregnancy rate. The purpose of this study was to evaluate the effect of shortening the dry period and the number of parturition and interaction between them, on health and reproduction and productive performance in Holstein dairy cow.
Materials and Methods 80 Holstein cows were used in a 2 × 2 factorial design from 56 days before to 56 days after calving. Cows (n=20) were randomly assigned to two groups on the basis of dry period length (56 or 28 days) and number of calving (two or three times of calving rate). The animals were fed three times a day. Dairy cattle rations based on the requirements was adjusted in the period before and after calving. Cows were milked three times a day and the amount of milk yield was recorded for six weeks. To determine the composition of milk, a mixture of daily milk was used and evaluated weekly. BCS, based on the system of five numbers was determined. Reproductive records including open days, pregnancy rate in four inseminations and days to first service was determined. The indicators of the uterine health of the cow containing metritis and endometritis incidence was assessed. Blood samples of cattle, on the day of entry into the study (56 days before the expectable calving), 28 and 7 days before calving and day 7, 28 and 56 after calving were measured. The concentrations of glucose, urea, triglycerides, total cholesterol, LDL-cholesterol, beta-hydroxy butyric acid (BHBA) and non-esterified fatty acids (NEFA) in the blood were measured. Data were analyzed by SAS software.
Results Milk yield was tended to be lower in group 28 than that in group 56 (P= 0.06). But milk composition and somatic cells of cows with 28 days dry period, does not have a significant difference with control group (56 days dry period). Means BCS after calving in the 28 days group, was lower than those of 56 day group (P