Influence of prolactin on foetal survival in rabbit does

Energy balance and reproductive performance in rabbit does

The mortality and the culling rates of females are very high in rabbit breeding. In many cases, the dead or culled females show low reproductive performances and poor body conditions. Energy deficit leads to body mobilization and reduced reproductive performance. Consequently, energy balance and lifespan are closely linked. Two in vivo methods to estimate body composition were recently validated for rabbit does. Ultrasounds and TOBEC methods permitted the evaluation of the changes in energy balance and their relationship to reproductive performance of females. Influence of intrinsic (parity, litter size, genetic line, ...) and extrinsic (reproduction rhythm, temperature, ...) factors on the energetic balance of females are discussed. Energy deficit and depletion of body stores occurring during lactation lead to a decrease in reproductive performance and the physiological mechanisms implicated in these effects were presented. Interest and limitations of several strategies to reduce the body energy deficit in reproducing does and to improve their fertility and thus lifespan are discussed: rearing, feeding, management, genetic selection. A multi-facetted approach, combining these various strategies seems to be required to meet these objectives.

Long term effect of post-weaning rhythm on the body fat and performance of rabbit doe

Reproductive protocols based on standard (Control: 11 days post-partum) or extended rhythm (PW: post-weaning at 27 days post-partum) were compared. Two groups of fifty 19-week-old New Zealand White females were inseminated for seven consecutive cycles. The kits were weaned at 26 days. On the day of AI, all the does were submitted to ultrasound scanning of the perirenal regions to measure fat thickness. The fertility rate and several indexes of efficiency were calculated. Fat thickness, estimated perirenal fat and live weight were higher in PW does. The does submitted to post-weaning rhythm had a higher sexual receptivity (P < 0.01), and fertility rate (P < 0.01) whereas litter size and pre-weaning mortality were not affected. Primiparous Control does showed a particularly low fertility rate; the value increased successively but was always lower than in PW does. PW rhythm in comparison with the standard one seemed more adapted to doe reproductive physiology even if there was a lower production (35.0 vs. 38.8 rabbit sold/year) and risk of fatness (18% of multiparous does).

Hormone profiles and nest-building behavior during the periparturient period in rabbit does

This study was done to elucidate the relationship between the hormones beta-estradiol, progesterone, prolactin and beta-endorphin and nest-building behavior in rabbit does during the periparturient period. Beta-estradiol increased as parturition approached with a significant increase starting 2 days before parturition (day -2). Progesterone decreased with the progress of gestation, but a significant decrease was observed starting on day -2. Prolactin concentration started to increase on day -2 prepartum but a significant increase in prolactin concentration was not noted until the last day of pregnancy. The concentration of beta-endorphin was highly variable during the sampling period and could not be correlated with the other hormones or nest-building behavior. To assess the role of prolactin in nest-building behavior, groups of rabbits were treated with bromocryptine, bromocryptine plus prolactin or saline (controls). Treatment with 4 mg bromocryptine or 4 mg bromocryptine + 1.5 mg bovine prolactin on days 25 and 27 of pregnancy did not affect the number of live kits born or the gestation length. The mean nest scores, a measure of the nest quality, were not affected by bromocryptine treatment, but treatment with bromocryptine plus prolactin resulted in lower nest scores (P < 0.05). Injection of 8 mg bromocryptine from day 28 of gestation to kindling resulted in an extended gestation (P < 0.05). Injection of 4 or 8 mg bromocryptine resulted in fewer live kits born (P < 0.05), reduced nest scores (P < 0.01) and blocked milk production, as determined from the palpable mammary tissue. These results indicate that prolactin has less influence on nest-building behavior than on milk production. The hormones most likely to influence nest building are beta-estradiol and progesterone because the levels of these hormones started to change at the time when the rabbits started to prepare nests. Further study is required to determine the influence of these hormones on nest-building behavior.

Effects of lactation, energetic deficit and remating interval on reproductive performance of primiparous rabbit does

Female rabbits (n = 151) were assigned at their first parturition (day 0) to one of three treatment groups (A: non-lactating does and ad libitum feeding, R: non-lactating does and restricted feeding, L: lactating does and ad libitum feeding). Additional females (n = 18) were slaughtered at parturition. Experimental females were presented to the male on days 3 (A3, L3 and R3 groups, n = 25, 26 and 26, respectively) or 10 (A10, L10 and R10 groups, n = 25, 25 and 24, respectively) and were slaughtered on day 28 after parturition. Compared to does slaughtered on day 0, adipose tissues were lighter in L (-66%) and R (-32%) females while they were heavier in A females (+40%; P < 0.01). These results suggest that both L and R females were in energy deficit. Receptivity (80% vs. 98%) and conception rate (51% vs. 83%) were lower in L compared to A females (P < 0.01) regardless the day of male presentation. Ovulation rate (-14%) and conception rate (-26%) were lower in R3 than in A3 does (P < 0.05). Ovulation rate was 24% lower in the L10 than in the A10 group (P < 0.01). The uterine contents were lighter (-25%) in L and R than in A does (P < 0.001) regardless the day of male presentation. These results suggest that the energy deficit associated with milk production can partly explain the negative influence of lactation on reproductive performance.

Influence of prolactin on in vivo and in vitro lipolysis in rabbits

Three experiments were conducted to assess the influence of prolactin on lipolysis in rabbits. In vivo, a single injection of 1 mg of ovine prolactin induces increased plasma glycerol and nonesterified fatty acids concentrations within 30 min (P < 0.01). On the contrary, in vitro, oPRL did not stimulate glycerol release in isolated adipocytes at physiological concentrations (under 10(-8) M). In a third experiment, the effect of chronic hyperprolactinemia on the adrenergic control of lipolysis was studied (daily subcutaneous injections of 1 mg ovine prolactin for 12 days). The weight of perirenal adipose tissue at the end of the period of injections was 27% lower in the prolactin-injected (PRL) rabbits than in the control (CTL) rabbits (88 +/- 15 g vs. 120 +/- 25 g; P < 0.05). Food intake during the period of injections was 28% lower in the PRL group than in the CTL group (177 +/- 21 g/d vs. 246 +/- 13 g/d; P < 0.05). Basal glycerol release was 157% higher in adipocytes from PRL rabbits than in those from CTL rabbits (P < 0.05). Stimulation of lipolysis with different adrenergic agonists was similar in both groups. These results suggested an indirect influence of prolactin on adipose tissue lipolysis in rabbits, but mechanisms implicated in this effect remain to be elucidated.