TRANSITION COW MANAGEMENT: CONSIDER THE RUMEN EPITHELIUM
It is well known the importance of the dry and transition period “setting” cows up for productive lactations. We are well aware of the dietary concerns during this period: DMI, energy consumption, mineral and vitamin levels as well as the abrupt diet change to a lactation ration. We know that with the dietary change from higher fiber, slower fermenting carbohydrates to more and faster fermenting concentrates that we need to allow time for the rumen microbial populations to adjust. What we, rather I, was reminded of is the physiologic changes required of the rumen itself, the rumen epithelium that is. What changes are required of the layers of tissue that make up the rumen wall during this time of dietary and metabolic change? A recent article by Martens et al (2012), discusses this topic.
The rumen wall is composed of a number of tissue layers, including muscle, connective tissue, and various cell layers functioning as ionic pumps. These cellular pumps perform the active transport of Na, Cl, Ca, Mg and HCO3- (buffer) secretion. The rumen papillae, finger like protrusions of the epithelium, provide maximal surface area for the passive transfer/absorption of VFA, water and urea. The entire rumen wall is a very thick and tough tissue (having eaten some while in Japan, let’s just say it is “chewy”) in order to churn 120L (100kg) of ingesta. Besides absorbing nutrients, this tissue must withstand the acidic conditions and remain intact in order to maintain a barrier to prevent toxins and microorganisms from entering the blood possibly causing infection and liver damage.
The dietary changes from dry to early lactation result in decreased pH, nearly 2x increase in VFA concentration requiring absorption as well as significant increase in osmotic pressure. The rumen epithelium must respond quickly to these changes. Some of these adaptive responses include:
1. Change in size and number of rumen papillae for increased nutrient absorption. Rumen papillae will shrink to 50% of their size during the dry period. Increasing the number and size of these papillae are the primary means of increasing absorptive capacity of the rumen on a lactation diet.
2. Cellular enzyme activity needs to increase for processing of nutrients during absorption.
3. Epithelial transport and barrier function need to increase. Managing nutrient uptake while withstanding the increased acidity of the rumen contents, which could impair the integrity of the rumen wall, possibly allowing bacterial infection.
The speed at which the rumen papillae can adapt varies and depends on which type of diets they are adapting to and from. Epithelial cell turnover can be 16d on a roughage diet of dry hay, 11d on a concentrate ration as measured in sheep. We know that butyrate helps to increase epithelial growth in vivo (in the animal), but is seen to inhibit growth in vitro (in the lab). Insulin and IGF1 increase epithelial growth. In general, it takes 6-8 weeks for full response of rumen epithelium to achieve a stable state of cellular proliferation when transitioned on to a lactation diet.
This article brought to light the thought of transition cows going off feed and what that may mean regarding rumen wall/epithelial health and how detrimental it can be for total health and productivity. Cows that go off feed in early lactation may risk damage to rumen tissue. Often times our response is to isolate or simply monitor the cow in the pen, yet provide the same TMR, same carbohydrate load, with possibly some nice dry hay. I wonder if getting cows back on feed requires a quicker response, quicker judgment to offer a more rumen friendly, “safer,” less rapidly fermentable carbohydrate diet sooner. This then made me think about our “steam-up” rations relative to not only the rumen microbial environment but also the rumen wall itself and the synergy required between animal and microbes when faced with dietary changes.
The authors acknowledge that there is a way to go before we fully understand the rumen epithelial response to dietary changes through the transition period. But we do know that adaptation of this tissue is critical in maximizing health and productivity of the lactating dairy cow.
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