PSI-8 - Impact of feeding level on boars from selection to entering the boar stud on trainability and growth measurements

Abstract: The objective of this study was to determine if restricting feed in boars at selection impacts growth of boars or training for semen collection. Twenty-five duroc boars randomly allotted at 6 months of age to receive one of two levels of restricted feeding(1.8 kg/d, n=12 or 2.72 kg/d, n=13) of a corn-soybean meal-based diet formulated to meet NRC(2012) requirements. Diets were fed for 9 weeks prior to training for semen collection where body weight(BW), body condition score(BCS), flank-flank tape measurements, Knauer sow caliper, loin muscle depth, backfat depth, and scrotal width and length were collected every three weeks. Training for semen collection was conducted 5 days/week for 2 weeks. Boars were given 10 minutes in the collection pen to successfully mount the dummy and start collection each training session. Training was scored on a scale of 1-5, 1=no interest and 5=successful collection. Three successful collections in a row boars were considered fully trained. All boars had their first production collection on wk 12. Data were analyzed using PROC MIXED and PROC FREQ chi-square in SAS 9.4 with boar serving as experimental unit. Weeks were analyzed individually and overall changes were evaluated. Significance was determined at P< 0.05 and a trend was observed at 0.05< P≤0.10. Boars fed 2.72 kg/d had increased BW on week 9 (P< 0.05) and week 12 (163.6 kg vs 149.8 kg, SE=2.17; P< 0.001), increased BW gain weeks 1-9 (P< 0.01), week 9-12 (P< 0.001), and overall (49.8 kg vs 34.4 kg, SE=1.60; P< 0.0001). The 2.72 kg/d boars also had increased backfat depth on week 9 (P< 0.01) and week 12 ( 8.4 mm vs 7.5 mm, SE=0.17; P< 0.001), larger caliper scores on week 12 (P< 0.01), higher flank-flank distance on week 9 (P< 0.01), and increased BCS on week 12 (3.2 vs 2.7, SE=0.14; P< 0.01). No differences were observed for loin muscle depth, or scrotal width and length. Feeding level did not affect trainability with approximately 92% of boars being trained at the end of the two-week period in both feeding levels. Boars fed 2.72 kg/d had increased semen volume (128 mL vs 81 mL, SE=12.1; P< 0.01) on their first production collection on week 12 with no effects on other semen quality parameters. Overall, feeding boars 1.8 kg/d for 12 weeks following selection resulted in lower body weight and composition measures indicating limit feeding boars at selection could be used to slow growth rates, potentially decreasing structural issues, and increasing longevity of growing boars in the boar stud, with no effects on training for semen collection. Future research is needed to investigate the long-term impacts of the degree of limit feeding growing boars following selection on lifetime semen quality and quantity.