Winter grazing on cotton stubble affects grazing behavior, feed intake, production, and health of small ruminants

Abstract

The effects of cotton (Gossypium barbadense Linn) stubble grazing during winter on the feed intake, grazing behavior, blood chemical parameters, production performance, and residual amount of free gossypol (FG) in animal products was investigated. Eighty adult ewes and twenty-five young goats grazed continuously on cotton stubble from sunrise to sunset for 90 d during the winter, without receiving any supplementary feed. We measured the biomass and components of cotton stubble before, and after 1 and 2 months of grazing; feed intake and grazing behavior at 1 and 2 months; and blood parameters and immunity indices at the beginning and end of the grazing period. The biomass of cotton stalk was 5486.08 kg/hm2 at the beginning and decreased to 4340.90 ± 917.10 kg/hm2 and 3599.09 ± 689.56 kg/hm2 after 1 and 2 months, respectively. The proportion of cotton leaves and boll shells in each component of cotton stalk decreased (P < 0.05). At 1 and 2 months, the walking time of ewes was 93.58 ± 3.08 min and 115.99 ± 2.25 min, and the distance covered was 6.80 ± 0.92 km and 10.20 ± 2.30 km, respectively; both increased during the late grazing stage (P < 0.05). At 1 and 2 months, the feed intake and dry matter digestibility did not differ (P> 0.05). The intake of digestible energy and digestible crude protein after 1 and 2 months in ewes was 7.91 MJ/d, 9.58 MJ/d, and 47.30 g/d, 69.04 g/d, respectively, which was lower than the nutritional requirements of grazing ewes. The blood platelet count and iron concentration at the end of grazing decreased (P < 0.05), whereas the concentrations of free gossypol (FG) and aspartate aminotransferase (AST) increased (P < 0.05). The grazing time of ewes accounted for over 60 % of the total pasture time. The total weight gain and average daily gain of goats grazing for one month were 6.65 kg and 0.23 kg, respectively, and were higher in the second month of grazing (P < 0.05). Hepatic congestion, hepatocyte necrosis, and tubular epithelial cell disintegration were observed in the liver and kidney. After grazing, goat blood FG residue was higher than before grazing (P < 0.05). Owing to the limited feed intake and digestibility of cotton stubble in winter, the demand for digestible energy and digestible crude protein in ewes cannot be satisfied by grazing alone.