Measuring behavioral and physiological responses to pain mitigation for ovariectomy in Bos taurus yearling beef heifers.

Ovariectomy (spaying) using the trans-vaginal dropped ovary technique (DOT) is performed to prevent pregnancy in cull female beef cattle that are not retained for breeding stock in areas practicing extensive grazing management. There are no reports describing analgesia for this surgical procedure. The objective of this study was to measure behavioral and physiological responses to determine whether an analgesic protocol of BXK [butorphanol (0.01 mg/kg), xylazine (0.02 mg/kg), and ketamine (0.04 mg/kg)] injected intramuscularly (i.m.) before spaying could mitigate procedural and immediate postsurgical pain, and whether oral meloxicam (1 mg/kg) administered at the time of spaying could mitigate postsurgical inflammatory pain. Forty-four red Angus and Angus crossbred yearling heifers (322 ± 27.0 kg BW) were randomly allocated to 1 of 3 groups: PALP (control; palpated but not spayed; n = 14), SPAY (spayed with no analgesia; n = 15), and BXKM (spayed with analgesia; n = 15). Behavioral measurements included visual analog scale (VAS) score, flight speed (FS), stride length (SL), and gait score (GS), as well as activity (lying, standing) and feeding behavior. Physiological measurements included salivary cortisol (SC), haptoglobin (Hp), serum amyloid A (SAA), substance P (SP), complete blood count (CBC), and rectal temperature (RT). Saliva and blood samples were collected, and RT, FS, SL, and GS were measured on day -1, day 0 (time of palpation/spaying), and hours 1, 2, 4, and days 1, 2, 4, and 7 after palpation/spaying. The BXKM heifers had lower SC concentrations than SPAY heifers at 1 h (P = 0.01) and 2 h (P = 0.004). Heifers treated with BXKM had Hp concentrations lower than SPAY heifers at 2 d (P = 0.01), 4 d (P < 0.001), and 7 d (P = 0.008), and lower Hp concentrations than PALP heifers at 4 d (P < 0.001). Concentrations of SAA were greater (P = 0.04) in BXKM heifers than in PALP heifers at 1 h and lower in PALP heifers than in BXKM heifers (P = 0.02) and SPAY heifers (P = 0.05) at 1 d. Heifers in the BXKM group had higher RT than PALP and SPAY heifers at 1 h (P < 0.001) and 2 h (P = 0.004). Results suggest that DOT ovariectomy is acutely stressful and painful and administration of BXK before spaying and meloxicam at the time of spaying mitigated the procedural and postsurgical stress, pain, and inflammation.