Adding condensed tannins to the diet increases ovulation rate in sheep

Abstract

The objective of the present study was to investigate whether adding condensed tannins (T) to the diet of sheep increases ovulation rate (OR). In all, 281 mature Polwarth ewes (49.9 ± 6.0 kg and body condition score (BCS) of 2.02 ± 0.24 units) were heat-synchronised (oestrus = Day 1) and sorted in the following four treatment diets: (1) native pasture alone (82.6 g of CP and 8.4 MJ metabolisable energy (ME)/kg DM) (NP; n = 70); (2) native pasture (NP) plus a supplement of 0.45 kg of soybean meal (S) from Day 10 to Day 14 (NP+S; n = 71); (3) NP plus a supplement of 0.45 kg S and 25 g of T, to get an estimated concentration of T in the diet of 1.5% (NP+S+1.5T; n = 69); and (4) NP plus a supplement of 0.45 kg S and 42 g of T, to get a concentration of T of 2.5% (NP+S+2.5T; n = 71). OR was measured 8 days after the second heat by rectal ultrasound (Day 25). The estimated consumption of crude protein (CP) during the supplementation period was 129, 261, 237 and 200 g/ewe.day for NP, NP+S, NP+S+1.5T and NP+S+2.5T ewes, respectively. NP+S+1.5T ewes had an OR of 1.90, which was higher (P < 0.05) than those for NP+S+2.5T and NP+S ewes (1.68 and 1.70, respectively). All supplemented ewes had a higher OR than did NP ewes (1.48, P < 0.05). Although NP+S+1.5T ewes ate less protein than did NP+S ewes, their OR was higher, as a result of a more effective use of the protein. The higher concentrations of 2.5% T in the diet might have not evoked a response in OR.