Effect of straw particle size in high grain complete pelleted diet on growth performance, rumen pH, feeding behavior, nutrient digestibility, blood and carcass indices of fattening male goats

Abstract

The study aimed to elucidate the effects of straw particle size of complete pelleted diet (CPD) on feed intake, growth performance, rumen pH, feeding behavior, selected blood metabolites, nutrient digestibility, and carcass attributes of fattening male goats. Sixteen male Beetal goats, averaging 27.0 ± 2.84 kg body weight (BW) were randomly assigned to one of the following dietary treatments (n = 8 male goats /treatment); 1) S4 (CPD having oat straw ground at 4 mm); 2) S8 (CPD having oat straw ground at 8 mm). The diets were iso-nitrogenous and iso-caloric with forage to concentrate ratio of 15:85, and were designed to achieve low NDF contents of 20% by adding 63% corn grains. The experiment lasted for 16 weeks; 2 weeks of receiving and diet adaptability period, 13 weeks of data collection, and last one week for nutrient digestibility. Animals were housed individually and fed the corresponding diet and water ad libitum. Feeding behavior was recorded on day 30, 60, and 90 of the study. Blood samples were collected weekly, whereas, rumen samples were collected on a bi-weekly basis. Total tract nutrient digestibility was performed at the end of the experiment. All goats were slaughtered to determine changes in the carcass attributes. Results revealed that DMI and ADG were higher (P < 0.0001) in the S8 group compared with the S4 group. The feed-to-gain ratio (F: G), however, was lower (P = 0.047) in the S8 group compared with that of the S4 group. Ruminal pH was higher (P < 0.0001) in S8 than S4 only at the beginning of the trial, with no later differences (P > 0.05). There was a significant treatment × week interaction (P < 0.05) for rumen pH during weeks 2 and 4 which remained below 6.0 in the S4 compared with the S8. The odds for diarrhea were 5 times lower in the S8 compared to the S4 male goats. Animals fed on CPD with the straw ground at 8 mm had higher (P ≤ 0.05) rumination time, DMI intake, NDF intake, and drinking time than those fed on CPD with the straw ground at 4 mm. Furthermore, the dressing percentage and marbling score was higher (P ≤ 0.05) in the S8 compared with the S4. The findings of this study suggested that the use of oat straw ground at 8 mm in a complete pelleted diet improved growth performance and carcass yield by improving the feeding behavior and stabilizing the rumen environment.