اثر زمان‌هاي مختلف تغذيه روي عملكرد گاوهاي شيري دو‌رگه در طي تنش گرمايي تابستان

بخش پرورش حيوانات اهلي در پاكستان يك موقعيت بي­نظير را در توسعه اقتصاد ملي اين كشور شامل مي­شود. مطالعه حاضر براي ارزيابي به كارگيري استراتژي كاهش استرس گرما از طريق استفاده از زمان­هاي مختلف تغذيه روي صفات عملكردي توليد و تركيب شير و خصوصيات فيزيكوشيميايي آن در گاوهاي شيري در طي فصل تابستان انجام شد. بيست رأس گاو هلشتاين فريزين به طور تصادفي در چهار گروه تيماري (G1: 80/20، G2: 50/50،G3 : 100/0 وG4 : 0/100؛ از نسبت­هاي روز به شب) تقسيم شدند. توليد و تركيب شير و خصوصيات فيزيكوشيمايي آن و سطح مالون­دي­آلدئيد در سرم خون تعيين شدند. نتيجه­گيري اينكه تغييرات در زمان تغذيه، به طور معني­داري توليد شير را در گروه­هايي كه در بخش خنك­تر روز تغذيه مي­كردند افزايش داد. تركيب شير و خصوصيات فيزيكوشيميايي آن نيز از نوسانات تغذيه در زمان­هاي صبح و عصر تأثير ­پذيرفته­اند. بنابراين، تغيير در زمان تغذيه در طي فصل تابستان در نواحي گرم يك روش عملياتي مناسب براي بر طرف نمودن اثرات تنش گرمايي روي عملكرد توليدي گاوهاي شيري است.

The livestock sector in Pakistan occupies a unique position in the national agenda of economic development. The current study was conducted to evaluate a heat stress mitigation strategy through different feeding times on the performance i.e. milk yield, milk composition and physiochemical properties of milk in dairy cattle during the summer season. Twenty Holstein Friesian cows (HF) were randomly divided into four groups (G1. 20/80, G2. 50/50, G3. 0/100, G4. 100/0 feeding at day/night %). Milk yield, milk composition, physiochemical properties and malondialdehyde (MDA) in blood serum were determined. In the first week morning time milk yield was significantly highest in group G1 followed by G2, G3 and G4, respectively. During the 2nd to 8th weeks in the morning time it was highest in G2 followed by groups G1, G3 and G4 followed. It was highest in G1 followed by G4, G3 and G2 in the evening time during 1to 8th weeks. In 5th week milk yield was more in G4, G3, G2 and G1 in the evening time. In all weeks (1 to 8) pH of milk was higher in groups G1, G2 and G4 followed by G3. In weeks 1 and 2, protein and lactose contents were similar among the four groups, while the fat percentage was higher in G4 followed by G3, G2 and group G1. In weeks 3 and 4 fat was more in the G4 and G3 groups respectively. In the third week pH, acidity and specific gravity of milk was not changed significantly in all the groups. In the fourth week pH was slightly reduced in G3, while acidity and specific gravity remained the same in all the groups. In group G5 pH and specific gravity of milk was comparatively high in group G1 followed by G2 and G3, while acidity was more in G1 as compared to other groups. Similarly pH and specific gravity of milk in the sixth week was slightly more in G1 followed by other three groups. In the seventh week fat was more in G4 followed by G3, G2 and G1. In week 1 levels of MDA were high in G4 followed by G3, G2 and G1. Similar results were found in weeks 2, 3, 4, 5 and 8. In the sixth and seventh weeks the level of MDA was high in G4 fol-lowed by G2, G3 and G1. It was concluded that changes in feeding time significantly increased milk yield in those groups which were fed in the cooler part of the day. Milk composition and its physiochemical properties were also affected due to variation in milk yield in the morning and evening times. Hence change in feeding time during the summer season in tropical areas is a good husbandry practice to mitigate heat stress effects on the production performance of dairy cattle.