اثر كوتاه‏كردن دوره خشكي بر عملكرد توليدمثلي و شيردهي در گاوهاي شيري هلشتاين با تعداد زايمان متفاوت

The effect of Shortening Dry Period on Lactation and Reproductive Performance in Holstein Dairy Cows with Different Parturition

برای ارزیابی بر هم‌ كنش طول دوره خشكی و تعداد زایمان بر تولید و تركیب شیر و فراسنجه‌های خونی، تعداد 80 راس گاو هلشتاین در قالب طرح فاكتوریل 2×2 استفاده شد. تیمار آزمایشی اول شامل دو دوره زمانی متفاوت از دوره خشكی یعنی 56 یا 28 روزه و تیمار آزمایشی دوم شامل تعداد زایمان گاوها یعنی یك بار زایمان در برابر دو بار زایش یا بیشتر بود. صفات مورد ارزیابی شامل بررسی عملكرد تولیدمثلی، شیردهی و وضعیت ایمنی و سلامت دام‌ها بود. گاوهای دارای طول دوره خشكی 28 روزه از نظر مقدار و تركیب شیر و سلول‌های پیكری تفاوت معنی‌‌داری با گروه 56 روزه نداشت. اما مقدار تولید شیر در شیردهی بعدی در گروه 28 روزه كمتر از گروه 56 روزه بود و این مقدار تمایل به معنی‌داری داشت (06/0P=). تغییرات امتیاز وضعیت بدنی پس از زایمان در دوره خشكی 28 روزه كمتر از گروه 56 روزه بود (05/0P <). روز اولین سرویس و روزهای باز در بین گروه‌های آزمایشی تفاوت معنی‌داری نداشت (37/0=P و 66/0=P)، اگرچه در گاوهای در گروه 28 روزه نسبت به 58 روزه كمتر بود. درصد آبستنی در نخستین سرویس و نیز در مجموع چهار سرویس در گروه 28 روزه نسبت به 58 روزه به ترتیب به طور معنی دار و غیر معنی دار بهتر بود. به نظر می‌رسد گاوهای با دوره خشكی كوتاه‌تر، توازن منفی انرژی كمتری را در دوره شیردهی بعدی تحمل كردند و در نتیجه عملكرد تولیدمثلی بهتری را در مقایسه با گروه با دوره خشكی متداول نشان دادند.

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 <0.05). The concentration of NEFA during postpartum in the cows with a dry period of 28 days, was less than the other group. The pregnancy rate in first service of cows with 28 days dry period was greater than that of cows with 56 days dry period. There were not any differences in blood chemical composition, and metritis and endometritis between two groups. Conclusion BCS in group with shortened dry period, has been decreased with little decay, because of reduced fat tissue mobilization. This might be diminished negative energy balance in cows in shortened dry period group and subsequently improved reproductive performance. It seems that reduced length of the dry period through a decrease of the volume of milk production, probably improved health and pregnancy rate at first insemination, and reduced days open and days to first service. It has seen suggested the improvements in negative energy balance, in shortened dry period cows caused to a less milk production peak, but this decreased amount was compensated somewhat in the period before calving in when animal did not suffer NEB. Thus, excessive pressure on cattle in the postpartum period is reduced. Evaluation of the effect of shortening the dry period on the performance of cattle during next lactation, can determine economic benefits or disadvantages of it in dairy herds.