Postpartum ovarian activity of Santa Inês lactating ewes fed diets containing soybean hulls as a replacement for coastcross (Cynodon sp.) hay

The Santa Inês, a Brazilian hair sheep, has a non-seasonal breeding activity. Data regarding the duration of the postpartum anestrous period in Santa Inês lactating ewes is lacking and the objective of this trial was to determine the effects of replacing neutral detergent fibre (NDF) provided by coastcross (Cynodon sp.) hay with NDF contained in soybean hulls (SH) on the postpartum ovarian activity--as measured by the serum progesterone (P₄) concentration. Fifty-six lactating ewes (body weight 56.1±6.8kg) were individually penned and used in a randomized complete block design with 14 blocks and four treatments. The SH NDF replaced 33 (SH33), 67 (SH67), or 100% (SH100) of the NDF contributed by coastcross hay in the control diet (SH0). This resulted in a SH inclusion at rates of 0, 25, 54, and 85% of the dietary dry matter (DM). Blood samples were collected twice weekly from the 14th to 84th day postpartum and the serum P₄ concentrations determined by radioimmunoassay (RIA). It was estimated that the 1st postpartum ovulation occurred 6 days before the date that a serum P₄ >=1ng/ml concentration was first recorded. The mean body condition score (BCS; 0-5 scale) was 3.0±0.19 on day 14 postpartum and the mean BCS at day 56 postpartum increased linearly (P <0.01) with the inclusion levels of SH (3.09, 3.24, 3.34, and 3.36, respectively). Treatments did not differ significantly in the induction of postpartum days to the resumption of ovarian luteal activity (34.1±15.3 days postpartum). On days 25, 50, and 75 postpartum 36, 80, and 100% of the ewes had resumed ovarian activity, respectively. Non-esterified fatty acid concentration decreased quadratically (P <0.05) with the SH inclusion, with values of 0.323, 0.244, 0.204, and 0.216mequiv./l for the SH0, SH33, SH67, and SH100 treatments being recorded, respectively. Replacement of the NDF provided by coastcross hay with the NDF from the SH did not influence the duration of the postpartum anestrous period in Santa Inês lactating ewes. Considering a 150-day gestation period and the 34 days postpartum anestrous demonstrated in the present study, the current production system of a lambing interval of 8 months (3 lambing events in 2 years) may not be optimizing the production potential and a system in which the lambing interval is shortened by at least 1 month may be feasible.