Digestibility and nitrogen balance of goats on high and low protein rations supplemented with a commercial tannin feed-additive

ABSTRACT

Despite the increasing importance of goat production in response to high demand for their products and their relative robustness to environmental stressors, and in contrast to other ruminant species, little data is available on how tannin extract feeding affects their feed intake, nutrient digestion and nitrogen (N) metabolism. Therefore, a trial in Oman investigated the respective variables by using a commercial tannin feed additive. In a 4 (treatments) x 3 (periods) x 2 (animals) Youden square, two weaned Batinah bucks each were fed a high or low protein diet of Rhodes grass hay and crushed barley grain, with or without the addition of a chestnut and quebracho tannin extract at 2 g/kg metabolic weight. Feed offered, feed refused and faeces and urine excreted were quantified to determine diet digestibility, total N excretion, N retention and rumen microbial protein synthesis (MPS). Due to their young age and low live weight, feed intake of goats was relatively low. Crude protein level and tannin addition had no statistically significant effect on dry matter (DM) and N intake, DM digestibility, N excretion in faeces and urine, as well as MPS. In consequence, no benefit of tannin feeding could be confirmed for the goats’ N retention, irrespective of diet composition. These results indicate, on one hand, an effective neutralisation of the tested tannin extract along the gastrointestinal tract of goats, but on the other hand, that stimulation of MPS or N retention by tannins cannot be evidenced when diet components are present that simultaneously release energy and protein, as is the case with barley.

KEYWORDS:

• Condensed tannins
• microbial protein synthesis
• small ruminants
• subtropical environment
• zero-grazing system

Acknowledgments

The authors are very thankful to Dr O. Alqaisi Shawabkeh and Dr W. Al-Marzooqi, as well as Mr A. Al-Abri, for their substantial support during the trial at the experimental farm of Sultan Qaboos University, Muscat, Oman, and to Prof. Dr A. Buerkert for facilitation of the study. We are very grateful to Prof. Dr U. Dickhöfer for her advice on the experimental design, provision of the analysis of purine derivatives and calculation of related results. The assistance of Mr H. Baumgärtner, Mrs C. Thieme, Mr C. Wagner, and Mrs E. Wiegard in sample analysis is gratefully acknowledged. This study was conducted in the context of the Research Training Group 1397 “Regulation of soil organic matter and nutrient turnover in organic agriculture”, subproject D2, funded by the German Research Foundation (DFG). The second author received financial support from Georg-August-Universität Göttingen.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This study was supported by Deutsche Forschungsgemeinschaft under the Research Training Group 1397 “Regulation of soil organic matter and nutrient turnover in organic agriculture”.