Induced seasonal reproductive performance in two breeds of sheep.

The objective of the present experiment was to determine whether failure to become pregnant through out-of-season reproductive management regimes is attributable to a failure to stimulate normal corpora lutea (CL) production. Romney ewes and East Friesian Composite (EF) ewes were mated in summer, autumn, winter, and early and late spring after administration of intravaginal progesterone inserts (plus eCG in spring and summer) in a factorial (two breedsxfive mating periods) experimental design. Oestrus rate was determined from mating data, and the numbers of CL were determined by laparoscopy 9 days after ram introduction. Conception rate, pregnancy rate and litter size were determined by transabdominal ultrasonography 62 days after ram introduction. Proportions of ewes displaying oestrus did not differ significantly (75-100%) between seasons or breeds, except for the Romney ewes in summer (67%; P<0.05). Numbers of CL on Day 9 for EF ewes was lowest in autumn (1.5) and winter (1.5), and highest in late spring (2.1; P<0.05). In contrast, Romney ewes had the lowest CL count in summer (1.3), and the highest in autumn (1.8) and winter (1.6; P<0.05). Only in summer was there a difference between breeds (EF 1.8; Romney 1.3; P<0.01). The proportion of ewes that failed to conceive despite having one or more CL present was highest in late spring (EF 41%, Romney 43%), and lowest in autumn (EF 9%, Romney 4%) and winter (EF 14%, Romney 4%; P<0.05). Conception and pregnancy rates followed similar patterns with values for autumn (EF 91%, 91%; Romney 96%, 96%) and June (EF 86%, 82%; Romney 91%, 83%) being significantly (P<0.05) higher than in early (EF 50%, 40%; Romney 54%, 50%) and late spring (EF 44%, 36%; Romney 42%, 36%). Pregnancy rate in summer was higher for EF ewes (60%) than for Romney ewes (39%) but conception rates were not statistically different (EF 68%; Romney 60%). Numbers of foetuses identified at scanning was highest in autumn (1.5) and lowest in late spring (0.5 P<0.001): Litter size in pregnant EF ewes was highest in early spring and lowest in winter (1.8 versus 1.2; P<0.01), but for pregnant Romney ewes was highest in winter and lowest in early spring (1.9 versus 1.3; P<0.001). It was concluded that seasonal differences in the ability of ewes to conceive are not the consequence of failure to display oestrus or to ovulate, but probably are a result of failure of fertilisation or the establishment of pregnancy.

The stress caused by laparoscopy in sheep and its alleviation.

AIM: To determine the plasma cortisol response to laparoscopy in ewes and investigate means of reducing it. METHODS: Ewes without lambs at foot (n=40) were subjected to one of three control or one laparoscopy treatments (n=10 ewes/treatment), being: no restraint or drugs; acepromazine maleate (ACP) control and no restraint; ACP and restraint in a cradle for 5 min; and laparoscopy following ACP. Additional ewes with lambs at foot (n=30) were subjected to: laparoscopy following ACP; laparoscopy following ACP and ketoprofen; and laparoscopy following detomidine. Drugs were injected 20 min before treatment, after a first blood sample had been taken. Blood samples were taken by jugular venepuncture from the ewes 20 min before treatment and at 20, 40, 60, 90, 120, 150 and 180 min after treatment, while all ewes were held in a pen. Plasma was harvested and assayed for its concentration of cortisol. RESULTS: Plasma cortisol concentrations (PCC) remained constant in ewes in the control restraint group for 80 min. In ewes given ACP, PCC increased for the first 20 min after treatment but then returned to pre-treatment concentrations. PCC of ewes given ACP and restrained in a cradle were elevated above pre-treatment concentrations for 90 min. PCC in ewes subjected to laparoscopy following sedation with ACP increased to a peak at 40 min and returned to pre-treatment concentrations after 60 (with lambs) or 120 (without lambs) min. When ACP and ketoprofen were given before laparoscopy, PCC peaked at 20 min and returned to pre-treatment concentrations by 40 min. PCC of ewes given detomidine before laparoscopy remained at pre-treatment concentrations throughout. PCC of ewes subjected to laparoscopy with ACP sedation only were greater than those of control restraint, ACP control, and ewes subjected to laparoscopy after being given ketoprofen or detomidine between 20 and 60 min after treatment. PCC of ewes subjected to laparoscopy were greater than those of control ewes placed in a cradle at 20 and 40 min. PCC of ewes given ketoprofen were lower than those of ewes subject to laparoscopy following ACP. CONCLUSIONS: Laparoscopy, even after sedation with ACP, caused some distress in ewes, as evidenced by increased plasma cortisol levels. Plasma cortisol response was alleviated by the administration of ketoprofen and eliminated by detomidine, probably because of both analgesic and sedative effects of the latter drug.