Effects of Betaine and Superdosed Phytase Supplementation on Semen Quality of Boars during and after Mild Heat Stress

The purpose of this experiment was to evaluate the effects of betaine and superdosing phytase on boar reproduction during mild heat stress. Twenty-seven mature, crossbred boars (Duroc x (York x Landrace)) were randomly allocated to treatment and were fed 2.6 kg/d of one of three corn, soybean meal diets that consisted of: 1) Control (CNT; 250 FTU per kg E. coli phytase; n = 9); 2) Betaine (BET; 250 FTU/kg E. coli phytase and 0.60% betaine; n = 9); and 3) Betaine and Superdosed Phytase (BP; 2500 FTU per kg E. coli phytase and 0.60% betaine; n = 9). The experiment was split into 4 environmental phases (4 wk/phase) consisting of pre-heat stress (PreHS; 26.0 ± 0.7℃ and 55.6 ± 2.2% relative humidity), heat stress (HS; 30.2 ± 0.7℃ and 55.6 ± 2.2% relative humidity), post-heat stress 1 (Post1), and post-heat stress 2 (Post2). Semen was collected weekly from each boar and was evaluated for semen quantity and quality parameters. Total motility, progressive motility, and percentage of morphologically normal sperm were reduced in the HS period (P < 0.001) with no effects from the dietary treatments (P ≥ 0.267). Overall, total sperm production (semen volume x concentration) did not differ among treatments (P = 0.986). Incidence of distal droplets was greater during HS compared to PreHS for CNT (P < 0.001), but not different for BET (P = 0.972) or BP (P = 1.000). This suggests that supplementation with betaine and superdosed phytase may reduce the effects of heat stress on specific morphological abnormalities, though total normal morphology did not differ due to the dietary treatments. The results of the present study show that even a mild heat stress can reduce boar semen quality characteristics. However, diets supplemented with betaine and superdosed phytase had little impact on improving semen quality and quantity in boars during mild heat stress.