Concentrate supplementation to Jersey cows grazing plantain and ryegrass

Abstract

Title: Concentrate supplementation to Jersey cows grazing plantain and ryegrass When compared to TMR-based dairy production systems, pasture-based dairy production systems produce milk at a lower cost per litre. Nutrients provided by a pasture species need to fulfil a major portion of the dairy herd’s nutritional requirements for the system to be successful. Kikuyu over-sown with ryegrass is the major herbage choice for pasture-based systems in South Africa's Southern Cape region. Climate and soil conditions are unpredictable, and the use of novel forage species is becoming ever more popular Plantain (Plantago lanceolate) is a perennial forage herb that can provide high amounts of high-quality forage. The forage herb is capable of adapting to drought and a wide range of soil conditions. The energy and mineral supply provided by plantain, decreases the need for high levels of concentrate supplementation. Plantain's low fiber content, however, may limit its application in pasture-based dairy production systems. The aim of this study was to see if milk production, milk solid production, body weight (BW), body condition score (BCS), and the rumen environment would stay the same or improve when Jersey cows grazing plantain during the day and ryegrass at night were given different levels of starch in dairy concentrates. The study was carried out at the Outeniqua Research Farm in the Western Cape region of South Africa, near George. Perennial ryegrass and plantain pastures were divided into equal blocks to facilitate the measurement of pre-and post-grazing yields for estimation of pasture intake. Fiftyone multiparous lactating Jersey cows were used in a production study. They were blocked according to milk production, days in milk (DIM) and lactation number and randomly allocated to three treatments (high-starch, medium-starch and low-starch containing 80%, 50% and 20% maize respectively) in a randomised complete block design. Maize content was reduced from the high- to the low-starch group, by replacement with high-fibre by-products (hominy chop, wheat bran and soybean hulls). A 14-day adaptation period was followed by 34 days of data collection. Each cow received 6kg (3kg at each milking) of their respective concentrate treatments per day on an ‘as-is’ xi basis and strip-grazed plantain from 06h00-13h00 and ryegrass from 14h00-5h00. The BW and BCS of cows were determined at the beginning and end of the study over two consecutive days. Milk yield was recorded daily for individual cows and milk samples were taken every second week to determine milk solid production; sample collection commenced after the adaptation period. For the rumen study, six additional rumen-cannulated cows were randomly allocated to either the high- or low-starch treatments in a two-period cross-over design. Rumen pH, volatile fatty acids (VFA) and rumen ammonia nitrogen (NH3-N) were determined and an in situ study was conducted to determine degradability of dry matter (DMd), neutral detergent fibre (NDFd) and the rate of NDF degradation (NDFkd). No differences (P>0.05) were found for milk yield and milk fat content between treatments and mean values were 20.9, 21.9 and 20.8 kg/cow/day and 4.88-, 4.91- and 4.90 % for the highstarch, medium-starch and low-starch treatment groups respectively. There was however a tendency for milk yield in the medium-starch group to be higher compared to the high-starch (P=0.10) and low-starch (P=0.07) treatments. Milk protein, milk lactose, somatic cell count (SCC), BW- and BCS change showed no difference between treatments (P>0.05). Milk urea nitrogen (MUN) was significantly higher in the medium-starch group compared to the low-starch group (P<0.05) and showed a tendency to be higher than the high-starch group (P=0.10). Ruminal pH, and individual VFA concentration, rumen NH3-N and the degradability parameters (DMd, NDFd and NDFkd) did not differ between the high- and low-starch treatments. There was however a tendency for total VFA to be higher for the low-starch treatment. It can be concluded that providing lactating Jersey cows with concentrate containing either 80-, 50- or 20% maize while grazing plantain and ryegrass caused no differences in production and ruminal parameters. It can be deduced that the medium-starch group performed best, because of the tendency for higher milk production. Lower cost associated with high fibre by-products compared to maize provides the opportunity for higher profit margins when feeding medium and low-starch levels as higher maize inclusion did not increase milk yield, milk fat or milk protein content.