عنوان مقاله [English]
Introduction Nowadays, many attempts were made to improve the supply of nutrients to calves and the importance of quality and quantity of calf nutrition, in order to stimulate the adequate consumption of feed for rumen development and achieve to suitable weaning weight at the optimal time and reduce feeding costs has been considered. Therefore, this study was conducted to investigate the effects of levels of starter protein and milk fed on feed intake, digestibility, weight gain and ruminal parameters.
Materials and Methods Forty newborn male Holstein calves (average body weight of 40±2 kg) were used according to a 2×2 factorial experimental design for 75 days. Feeding the colostrum was performed immediately after birth for 3 days. Calves were randomly divided into 2 groups(n=20); first group was fed with whole milk with the amount of 10% of their body weight (BW), while the second group was fed with whole milk with the amount of 7% of their BW. These 2 groups were divided into sub-groups of calves (n=10 for each) again. One of these sub-groups was fed with starter diet containing 20% crude protein (CP), while the other sub-group was fed with starter diet containing 17% CP ad libitumas the starting feed. The rations were iso-energetic. Water and calf starter were offered free choice. Ruminal fluid samples were collected by esophagus tube after morning feeding on days 30, 60 and 75. Feed intake and calves weight were measured daily and weekly respectively. Statistical analysis was performed using the mixed procedure of SAS software. Treatments means were statistically compared by the test of Duncan.
Results and Discussion The results showed that feed intake, daily weight gain, feed conversion, apparent digestibility of nutrients and ruminal fluid pH was not affected by amount of milk fed and starter protein levels. Although, there were no significant differences between amount of milk fed and protein level of starter on weight gain, but average weight gain was higher in calves fed milk as 10% BW than those fed 7% BW at before weaning. Effect of day was significant on feed intake and daily weight gain at total period and before weaning respectively. Before weaning, the effect of week was significant on feed conversion and the effect of day and interaction between day and starter protein level were significant on daily weight gain. After weaning, feed conversion was not affected by treatments. Interaction between starter protein levels and amount of milk fed were significant for apparent digestibility of dry matter, fat, NDF and ADF. Digestibility of crude protein was not statistically significant between treatments. Amount of feed intake, passage rate of solid materials, rumen microorganisms population can change digestibility of nutrients. Effects of amount of milk fed, starter protein levels and their interactions were not significant on ruminal fluid pH. Rumen ammonia-N concentration was affected by starter protein levels on day 30. But, interaction between day and starter protein level was significant on rumen ammonia-N concentration on day 75. No difference in rumen ammonia-N concentration was observed on day 60. Rumen ammonia-N concentration increased with the starter containing 20% CP. Effect of starter protein levels, amount of milk fed and their interactions on acetic acid and butyric acid concentrations were not significantly different between treatments (P> 0.05). Propionic acid concentration was not significantly different between treatments (P> 0.05). Effect of starter protein levels on the total volatile fatty acid concentration was statistically significant (P< 0.05). Passage rate of solid materials of rumen and the proximal of digestive tract (%/h) were not significantly different among the treatments. Treatment 1 (CP =17% and milk intake = 7% of body weight) and treatment 3 (CP =20% and milk intake= 7% of body weight) had the highest and the lowest solid passage rate in digestive tract. Passage rate of solid materials increased and retention time of solid materials decreased with increased feed intake in calves. Interaction between amount of milk fed and starter protein level was significant on total retention time of solid materials in the digestive tract. Treatment 2 and treatment 1 had the highest and the lowest total retention time of solid materials in the digestive tract and this subject was one of the reasons that caused differences in digestibility of nutrients between treatments.
Conclusion In this study, when amount of milk fed increased, daily weight gain and feed conversion improved and feed intake decreased (numerically). Calf starter containing 20% crude protein had any significant effect difference on performance. Satisfactory growth of young calves from birth to two months of age can be achieved by starter protein level 17% (lower than NRC recommended) if dry matter intake adequate. Calves were fed with whole milk with the amount of 10% of their body weight, their feed intake decreased after weaning. Results showed that, body weight gain, feed conversion, digestibility coefficients of nutrients in treatment 2 was better than other groups.