Hormonal changes in relation to productivity of pregnant rabbit does

Abstract

Pregnancy is a critical period for animals where it undergoes many physiological changes including hormones, which are not received a great attention in rabbit. Therefore, a total number of 25 New Zealand White pregnant rabbit does were used, to assess the changes in concentration of relevant hormones in relation to rabbit productivity. Blood samples were collected on 14, 21 and 28 days of pregnancy and on kindling day to quantify six maternal hormones. Litter size and weight, in addition to average of weekly and total milk yield were determined. Concentrations of the six hormones during the second half of pregnancy ranged between 3.2 to 4.0 ng/ml for progesterone (P4), 47.3 to 89.0 pg/ml for estrogen (E2), 2.0 to 3.7 ng/ml for prolactin (PRL), 114.5 to 136.8 ng/ml for insulin like growth factor-I (IGF-I), 36.0 to 39.2 ng/ml for thyroxine (T4) and 1.9 to 2.2 ng/ml for triiodothyronine (T3). The corresponding values on kindling day were 1.6 ng/ml, 26.8 pg/ml, 4.6 ng/ml, 131.6 ng/ml, 37.4 ng/ml and 0.9 ng/ml, respectively. At day 14, maternal P4, E2, PRL, T4 and T3 were the lowest, whereas IGF-I was the highest compared to the other two days of pregnancy. At day 28, levels of E2, PRL, T4 and T3 were the highest in comparison with days 14 and 21 of pregnancy. On kindling day, P4 and T3 showed the minimal levels, whilst PRL exhibited the maximal level compared to the levels at all the gestational days. The relationship among the different hormones had various trends. The average of total milk yield (129.9 g/d) was negatively correlated with both P4 and E2, and positively associated with the PRL, IGF-I, T4 and T3 hormones. Furthermore, litter size was positively related with P4, E2 and PRL, and negatively with T4, T3 and IGF-I. Whereas, litter weight was negatively correlated with P4, E2 and T4. We recommend giving more attention to the rabbit doe reproduction, particularly close to parturition to achieve good economical return. However, further studies are urgently needed in this area.