Effect of dietary factors on rumen metabolism and the microbiome in high yielding dairy cows

Johnson, C. (2022) Effect of dietary factors on rumen metabolism and the microbiome in high yielding dairy cows. Doctoral thesis, Harper Adams University.

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Previous work has established that poor diet mixing, diet selection and short-term feed restriction (FR) are common on many UK dairy farms. When cattle sort through a total mixed ration they can alter both their level and pattern of concentrate intake which can increase the risk of subacute rumen acidosis (SARA), although the effects on rumen metabolism and the microbiome are unclear. Periods of short-term FR can occur due to a shortage of the ration, machinery malfunction, or poor management, and when cattle re�feed they can overeat concentrates increasing the risk of SARA, defined as periods of pH depression lasting more than 5 to 6 h/d with rumen pH <5.8. Supplementing the diet with a live yeast is common practice in ruminant nutrition to improve rumen conditions as yeasts can increase rumen pH by promoting lactate utilising bacteria growth and scavenging oxygen from the rumen which can compromise fibrolytic bacteria activity. There is a lack of understanding of the precise effects of live yeasts on rumen metabolism and the microbiome in dairy cows. There is interest in increasing the nitrogen efficiency of dairy cows along with reducing ammonia emissions from dairy farms. Feeding Yucca schidigera (De-Odorase® ) is more common in monogastric animals to reduce volatile ammonia emissions from slurry into the environment, however, its effects on rumen metabolism, the microbiome and nitrogen efficiency in dairy cows is unclear. The objective of the thesis was to determine the effect of pattern of concentrate allocation, short-term FR and supplementation with live yeast or Y. schidigera on rumen metabolism, the microbiome, and performance of high yielding dairy cows. In the first study changing the pattern of concentrates fed (even/uneven) had little effect on performance or rumen metabolism, while yeast supplementation tended to increase rumen pH, rumen ammonia concentration and the relative abundance of operational taxonomic units (OTU) related to Clostridiales, associated with fibre degradation. In the second study, a FR period followed by re-feeding decreased dry matter intake (DMI) by 5.14 kg/cow/d during FR and increased by 4.96 kg/cow/d on recovery day 1 (rec d1) compared to the baseline, whilst milk yield decreased in the recovery period, returning to baseline levels after four days. Rumen pH and ammonia concentration also decreased during the recovery period. Following FR the relative abundance of Methanobrevibacter and lactate producing bacteria Bifidobacterium longum increased, and with yeast supplementation Treponema bryantii abundance increased during the recovery period. In the final study supplementing the diet with Y. schidigera had a greater effect on the microbiome than live yeast. Supplementation of Y. schidigera along with a live yeast decreased DMI but had no effect on milk yield, whole tract digestibility, plasma metabolites or rumen metabolism. Supplementation of Yucca schidigera tended to decrease slurry pH compared to the Control after 6 h which may reduce volatile ammonia loss, although ammonia losses from slurry were similar between treatments. In conclusion, common issues on farm such as diet selection, short term FR v and feeding diets high in RDP can have negatives effects on performance, rumen metabolism and the rumen microbiome, and therefore measures should be taken to avoid occurrence on farm. When supplementing the diet with a live yeast in conjunction with these situations, the effects of yeast on performance and the rumen microbiome were inconclusive

Item Type: Thesis (Doctoral)
Divisions: Agriculture and Environment (from 1.08.20)
Depositing User: Ms Kath Osborn
Date Deposited: 13 Sep 2022 11:21
Last Modified: 13 Sep 2022 11:21
URI: https://hau.repository.guildhe.ac.uk/id/eprint/17881

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