Review/Oorsig Volume 22, Issue 01 - Page 7

Volume 22 • Issue 01 • 2018 more alkalotic (higher pH) rumen environment negatively affects NDF degradation, DMI from pasture and the absorption of essential nutrients like magnesium, which is necessary for energy and calcium metabolism. Excess NFC leads to a fall in rumen pH, which is a less favorable environment for cellulolytic bacteria to function in. This may happen when cattle consume abundant amounts of carbohydrate-rich supplements or, for example, soon after being turned out onto maize stover lands where they pick up many cobs. This will lower NDF degradation, passage rate and DMI. If less DM is consumed per day, less beef will be grown – leading to a lower income. Rumen bacteria need soluble and degradable protein to meet their N requirements. The degradable protein requirement is for supporting optimal utilization of NFC and FC to meet respective microbial growth requirements. The rate of microbial growth of each category is directly proportional to the rate of carbohydrate digestion, so long as a suitable nitrogen source is available. The extent of digestion in the rumen depends on digestion of FC and NFC feed fractions and how rapidly the feed passes out of the rumen. In the early grass growth season it may be faster than during the late winter – as is evident from faecal consistency being loose or firmer, respectively. The extent of digestion thus depends on factors such as level of intake, particle size, rate of hydration, lignification, and characteristics of each carbohydrate and protein fraction. Veld and supplement management during the dormant season (autumn, winter) and their effect on rumen health Estimation of the available pasture DM left in the “pantry” at the end of the grass growing season (onset of the dormant season) gives an indication of DM available during the dormant season – until new grass yield becomes available in the next growing season. This must be matched with the number of animal units (1 AU = 450kg) to be “over-wintered” – each requiring about 10kg DM daily. Timely destocking at the start of the dormant season is a critical action to prevent running out of pasture DM – which will lead to a loss in condition during late gestation. This results in an increased ketone body concentration in serum which is mirrored in the follicular fluid and will affect oocyte quality. Nitrogen, more specifically RDP, is the most limiting nutrient to the rumen microbes in winter – especially on sourveld. Apart from RDP, rumen bacteria need an adequate source of fermentable carbohydrate to incorporate NPN into microbial protein. Microbial protein is essential for the dry, mid-pregnant cow to efficiently regain body fat reserves that were lost during the previous lactation. This gain in body fat reserves should take place well in advance of the last 2 months before calving. The biological value (BV; amino acid balance for gain of body fat reserves) of microbial protein is almost ideal for the pregnant cow, which at this stage of her production cycle (4-7months pregnant) has a relatively low nutrient requirement. Winter supplement intake must always be closely monitored. Knowing the average N concentration of winter pasture and the DMI thereof, one can calculate the percentage total crude protein (TCP) as well as RDP intake from the total diet DM. Rumen bacteria will be compromised in their function should the TCP of the final diet DM be below 70g/ kg (7%). If winter supplement intake is excessive, it may be as a result of i nsufficient pasture DM availability – i.e. the cattle are hungry. This may lead to rumen alkalosis should RDP intake be too high. Fecal consistency is a handy indicator of rumen function and fiber degradation with dry, hard feces being an indicator of poor microbial degradation of fiber – leading to a slow passage rate of ingesta. Veld and supplement management during the growth season and its effect on rumen health The primary objective is to supply Phosphorous (P) for both rumen microbes AND the lactating cow – which must re-conceive in this period. P is required for efficient energy metabolism – which is essential to prevent an excessive 7