The use of encapsulated condensed tannin extract and β-carotene supplementation to manipulate oxidative status, production and reproduction performance in sheep

Abstract

The study aimed to investigate the supplementation effect of Acacia mearnsii tannin extract and ß-carotene on the production and reproduction performance of sheep. To achieve this aim four studies (two experiments, one meta-analysis and one literature review) were conducted with the following specific objectives: The objective of study 1 was to investigate the supplementation effects of Acacia mearnsii tannin extract (TE) and encapsulated tannin extract (ETE) on reproduction performance and oxidative status of South African Mutton Merino rams. The objective of study 2 was to perform a meta-analysis to identify the threshold level of tannin extracts (black wattle, quebracho, and chestnut) on feed intake and digestibility in sheep and cattle. Study 3 was conducted to evaluate the effects of ß-carotene supplementation and age on the oxidative status of grazing merino ewes during breeding, pregnancy, parturition and early lactation as well as on their production and reproduction performance. The objective of study 4 was to review the literature to assess the effects of below and above requirement ß-carotene supplementation on the production and reproduction performance of female goats and sheep. In the first trial, thirty merino rams were divided into five groups: 0.0 g TE (control), 1.5 g TE, 3 g TE, 1.5 g ETE, and 3 g ETE supplemented daily for 16 weeks transiting from autumn to winter. Bodyweight and testicular measurements were recorded biweekly. Semen and blood samples were collected weekly during the last five weeks of supplementation. In the second trial, 104 ewes were divided into four groups drenched daily with 100 mg, 75 mg, 50 mg or 0.0 mg (control) of ß-carotene in a completely randomized block design. Supplementation lasted 28 days before oestrous synchronization; 14 days during oestrous synchronization (CIDR) and hand-mating; 18 days post-hand-mating; 30 days before lambing and 15 days after lambing. All animals were grazed on Kikuyu grass (Pennisetum clandestinum). Six ewes from each group (total = 24) were plasma sampled to measure oxidative and hormonal status during the experiment. The data for the meta-analysis were extracted from forty-three peer-reviewed articles and one PhD thesis that met the selection criteria. We proposed and used the change percentage to calculate the responses of the dependent variables to the inclusion of TE. The change percentage compares the tannin-treated group with the control group in each study. Therefore, feed intake, digestibility parameters, N balance parameters, and weight gain were calculated in response to the addition of TE in each applicable study. Statistical analyses of the data were performed using the RStudio integrated tool. Study names were treated as random effects, whereas TE level, TE type or source, animal species and supplementation period were treated as fixed effects. Data used to review the supplementation effect of β-carotene on the production and reproduction performance of female sheep and goats were extracted from thirteen peer-reviewed published articles that met the selection criteria. We estimated the animal requirement for β-carotene, the amount of β-carotene provided to the animal in the diet and the amount of β-carotene supplementation used in each study. Those estimations were done to indicate whether the diet fulfils the animal requirement of β-carotene or not. Results showed that the increase in the ETE from 1.5 to 3 g/animal/day increased the testicular length and sperm concentration, as well as decreased the percentages of low and non-progressive spermatozoa (p < 0.05). Simultaneously, the increase in the TE from 1.5 to 3 g/animal/ day decreased semen volume and elevated the percentage of abnormal sperm (p < 0.05). The results suggest that the encapsulation of TE affords the maximum benefit of the TE on sperm quality. Treatments with TE and ETE did not affect the hormonal and oxidative status. Testicular measurements were significantly higher in autumn compared to winter. The plasma level of cortisol significantly correlates negatively with sperm motility, viability, and acrosome integrity. The results of the meta-analysis showed that tannin sources and tannin type had no significant effect on feed intake, and the level of 3.5 g/100 DM is suggested as the TE threshold for feed intake in sheep and cattle. The levels of 5.7, 2.5, and 2.7 g/100 g DM are proposed as organic matter digestibility (OMD) thresholds for chestnut, quebracho and black wattle TE in sheep and cattle, respectively. The levels of 1 g and 2.3 g/100 g DM are proposed as the crude protein digestibility (CPD) thresholds for TE in sheep and cattle, respectively. The levels of 2.4, 2.5, and 0.5 g/100 g DM are proposed as neutral detergent fibre digestibility (NDFD) thresholds for chestnut, quebracho, and black wattle TE, respectively. For acid detergent fibre digestibility (ADFD), the thresholds were 3.2 and 1.8 g/100 g DM for chestnut and quebracho, respectively, while only 1 g/100 g of black wattle TE decreased ADFD by 15%. Our meta-analysis revealed that the CP digestibility model has the strongest and most accurate prediction of the response to TE inclusion compared to the other digestibility parameters studied (OM, NDF and ADF). Therefore, based on the CP digestibility response, we propose to consider 1 and 2.3 g/100 g DM TE as thresholds for digestibility in cattle and sheep, respectively. The proposed thresholds showed a negligible effect on weight gain in cattle and sheep after ingestion of TE. This study is the first to report that supplemental β-carotene above 75 mg/animal/day may act as a pro-oxidant in ruminants under oxidatively stressed conditions such as parturition. Age did not affect the oxidative status of the ewes. The supplemental ß-carotene did not affect bodyweight, oestrous parameters, corpus luteum size, conception rate and litter size. The supplemental β-carotene or age did not affect the lamb’s survival rate or weight at birth or 15 days old. The survival rate of singles and twins is higher than that of triplets and quadruplets. Older ewes (4-6 y) showed earlier and longer duration of oestrus than the younger ones (1-3 y). The finding of the review work showed that β-carotene supplementation enhances the production and reproduction performance of the sheep when fed on a carotene-deficient diet. β-carotene supplementation may increase the levels of some hormones such as progesterone in the blood of sheep and goats when fed on a diet that fulfils their requirements of β-carotene. However, this supplementation of β-carotene above the requirements seems to not affect the production and reproduction parameters such as body weight, milk production, oestrous parameters, conception rate, pregnancy rate, and litter size. The results of this study provide more insight into the optimum application of supplemental tannin extract and ß-carotene as a source of antioxidants in ruminants in general and in sheep in particular.