Effects of partial replacement of concentrate with feed blocks on nutrient utilization, microbial N flow, and milk yield and composition in goats

Two experiments were carried out to evaluate the effect of partial replacement of concentrate with 2 types of feed blocks (FB) on rumen protozoa numbers, nutrient utilization, microbial N flow to the duodenum, and milk yield and composition in goats. The concentrate included oat, corn grain, barley, soybean meal, salt, and vitamin-mineral mixture. The FB (types I and II) were composed of crude 2-stage olive cake (120 or 100 g/kg), fava beans (0 or 400 g/kg), barley (320 or 200 g/kg), beet molasses (220 or 100 g/kg), sunflower meal (180 or 0 g/kg), quicklime (70 or 90 g/kg), salt (60 g/kg), urea (0 or 20 g/kg), and vitamin-mineral mixture (30 g/kg). In experiment 1, 6 adult, dry, nonpregnant, rumen-fistulated Granadina goats (46.9 ± 2.15 kg of BW) were used and 3 trials were carried out. In each trial, 2 goats were randomly assigned to receive 600 g of alfalfa hay and 400 g of concentrate (diet AC), 600 g of alfalfa hay, 200 g of concentrate, and FB I (diet ACBI), or 600 g of alfalfa hay, 200 g of concentrate, and FB II (diet ACBII) with 6 replications per diet. The FB were supplied ad libitum. The ratio of purine bases to N was higher in solid- and liquid-associated bacteria for FB goats than for AC goats. In experiment 2, 18 Granadina goats (39.6 ± 1.89 kg of BW) in the middle of the third lactation were used, and 3 trials were carried out by following a 3 × 3 Latin square experimental design. In every trial, 6 animals randomly received 1.0 kg of alfalfa hay supplemented with 1.0 kg of concentrate (diet AC) or 0.5 kg of concentrate and FB I and II (diets ACBI and ACBII) with 18 replications per diet. The FB were supplied ad libitum. The intakes of organic matter and fat were higher with the AC diet than with the FB diets. The intake of acid detergent fiber was higher for FB-containing diets than for the AC diet. The neutral detergent fiber digestibility of FB diets was higher than that of the AC diet. Energy intake was higher for diets AC and ACBII than for ACBI. Microbial N flow was affected by diet. Milk yield was higher in goats fed the AC diet than in those receiving the FB diets. Conjugated linoleic acid content was higher in milk from FB than in milk from AC goats. Our study suggests that FB type II based on local ingredients could be used advantageously to reduce half of the amount of concentrate without detrimental effects on nutrient utilization, N value of the diet, and milk composition. The decrease of milk yield with ACBII compared with that obtained with the AC diet could be compensated by better quality of milk, decreased cost of feeding, and environmental advantage derived of including by-products in FB.