Crude protein levels in diets containing pelleted concentrate for lactating goats: intake, digestibility, milk production and composition

Resumo

This study aimed to evaluate the effects of crude protein (100, 130, 160 and 190 g kg-1 of dry matter) of diets composed of 200 g kg-1 of Tifton 85 grass hay and 800 g kg-1 of pelleted concentrate on intake, nutrient digestibility, production and composition of milk in lactating goats. Eight female Saanen goats with 42.7 ± 1.43 kg and 57.7 ± 7.37 days of lactation and milk production of 2 ± 0.22 kg at the beginning of the experiment were housed in individual 1.32 × 3.10 m stalls and distributed into two 4 × 4-balanced Latin squares. Intake of dry matter, organic matter, crude protein, neutral detergent fiber corrected for ash and protein, ether extract and total digestible nutrients showed a quadratic effect, with maximum intake of 2.030; 2.000; 305; 769; 55 and 1.574 g day-1 at the levels of 140.7; 140.8; 189.2; 140.9; 144.9 e 142.7 g kg-1 DM, respectively. Digestibility of dry matter, organic matter, crude protein, non-fibrous carbohydrates, ether extract and total digestible nutrient level varied linearly, with increases estimated at 0.54; 0.50, 2.02, 0.49, 0.80 and 0.63 g/100g for each percentage unit of protein added to the diet, respectively. Milk production was affected, with increase of 0.54 g for each 1% crude protein added to the diet. Milk lactose level decreased linearly, unlike the fat level, which increased linearly. Protein level showed a quadratic behavior, with a maximum of 36.7 g per kg of milk at the level of 160.5 g per kg of DM. It is recommended to use crude protein between 135 g and 150 g per kg of dry matter of diets consisting of 800 g of pelleted concentrate (composed of soybean meal replacing the alfalfa hay as protein source) per kg of DM for lactating goats producing 2 kg of milk per day.