بر عملكرد گاو شيري NRC و AFRC مقايسه تاثير ميزان انرژي و ژروتيين پيشنهادي

Comparison of AFRC and NRC systems in energy and protein requirement for dairy cow

The effect of feeding protein and energy according to the AFRC (1993) and NRC (2001) recommendations on dry matter intake, digestibility, milk yield and milk composition was studied in Holstein dairy cows. The study included a feeding and digestion trial. The feeding trial was conducted using 10 multiparous cows in mid lactation in a completely randomized design. The cows were divided into two groups of five cows. Group (I) received an AFRC diet and Group (II) a NRC diet. The duration of the trial was eight weeks. The diet consisted of wheat straw, alfalfa hay, corn silage, barley grain, wheat bran, cottonseeds meal and sugar beet pulp with molasses. The digestion trail with indirect method for estimating digestibility of diets consumed by dairy cattle with chromic oxide as an indicator. The dry matter intake for Gp I and Gp (Il) was 20.3 and 21.12 kgd^-1, respectively. The milk and 4% FCM yield (kgd^-1) for the corresponding two groups were 24.5, 23.9 and 23.11, 22.25. The protein, fat, dry matter contents (%) for Gp I and Gp II were 3.52, 3.69, 12.74 and 3.59, 3.68, 12.73 respectively. The difference between the two groups in DMI, body weight gain, milk yield and milk composition was not significant (p>0.05). The digestibilities of dry matter and crud protein of two diets were similar. The results indicated that CP% level according to NRC (896gr) higher than AFRC; it had no beneficial effect on DMI, milk yield, milk composition and body weight gain. Therefore, it is concluded that in Holstein dairy cows, with medium levels of production, feeding protein and energy according to AFRC recommendations is adequate.