Effect of diet concentrate level and fattening period duration on growth performance, nutrient digestibility, and rumen parameters in male Lori-Bakhtiari lambs

In this study, the effect of forage:concentrate ratio on growth performance, nutrient digestibility, and rumen parameters in male Lori Bakhtiari Lambs was investigated. A total of 27 male lambs (70 ±15 days of age, mean live weight of 26.3 ± 3.3 kg) were fattened for three months with three different levels of concentrate (55, 70, and 85%) and three different fattening period duration (first, second and third months). The apparent digestibilities of rations were measured monthly using acid-insoluble ash as an internal marker. Ruminal fluid samples were taken to determine the ruminal fermentation parameters at the end of each month. The results showed that increasing the level of concentrate improved daily weight gain and decreased feed conversion ratio (P<0.05). Increasing the diet concentrate level resulted in a decreased ratio of acetate to propionate and isobutyric acid concentrations (P<0.05). The ratio of acetate to propionate and daily weight gain decreased with increasing fattening period duration (P<0.05). In contrast, feed conversion ratio, ammonia concentration, and protozoa count increased. Interactions between diet concentrate level and fattening period duration had significant effects on final body weight, feed intake, nutrient digestibility coefficients, propionic acid concentration, and acetate:propionate ratio (P<0.05). In conclusion, the positive effects of concentrate level on performance, nutrient digestibility, and volatile fatty acid production were affected by the duration of the fattening period. Therefore, it is better to shorten the duration of the fattening period when using a high concentrate diet, and the maximum dietary concentrate level should be equal to 70% if the duration of the fattening period is increased.