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TO WHAT EXTENT CAN CITRUS PULP REPLACE MAIZE IN THE DAIRY COW CONCENTRATE?

Discipline: feeding/nutrition; Key words: Fruit waste, maize alternatives, pasture degradability, starch, supplementation. 

Supplemental concentrate feeding is often used to increase milk production from pasture. To that effect, cereal grains form the largest part of the concentrate supplement, but with their high starch content lactic acid is produced resulting in low pH and impaired microbial activity. A way to address the problem is to partially replace the cereal grain with carbohydrates which contain less starch, but are still highly digestible. To be highly digestible fibre must be low. Low-fibre carbohydrates may contain sugar and pectin and they have been shown to have a more positive effect on the rumen environment and maintain production when they replace cereal grains in TMR systems. Dried citrus pulp (DCP) which is such a product is a by-product of the juicing industry and is high in sugar (208 g/kg dry matter [DM]) and pectin (150–200 g/kg DM) and low in starch (174 g/kg DM). The inclusion of DCP in dairy rations is common practice in TMR systems, where it acts as a flavour enhancer owing to the high sugar content, promoting feed intake. No previous work has been documented on the use of DCP as a feed source for cows grazing pasture. The aim of the study cited below was therefore to determine how effectively maize could be replaced with DCP in a concentrate supplement to Jersey cows grazing ryegrass. 

In the study, maize was stepwise replaced with DCP in the concentrate supplement and the effect measured on milk yield, milk composition and rumen health. Sixty-eight lactating Jersey cows (about 85 days in milk with a mean daily milk yield of 20.5 kg) were used in the trial. The cows were allocated to one of four treatments, with 17 cows per treatment, namely no DCP (NDCP): 0% replacement; low DCP (LDCP): 33% replacement; medium DCP (MDCP): 66% replacement; and high DCP (HDCP): 100% replacement. An additional six ruminally cannulated Jersey cows were randomly allocated to the NDCP and HDCP treatments in a two-period cross-over design to study the effects on the rumen environment. 

Milk yield decreased between 2.1 and 3.2 kg/day when maize was replaced with DCP. Milk fat content did not differ between treatments. However, treatment had a quadratic effect on milk protein and lactose content, with the LDCP and MDCP treatments having the highest values. No change in the diurnal ruminal pH curve and no differences in the rate and extent of pasture dry matter and neutral detergent fibre degradability between treatments were observed. In general rumen health and activity were maintained. It was concluded that the use of DCP as a replacement for maize in a concentrate supplement in pasture systems should be considered only if DCP is available at a lower cost than maize, as this will make up for the decrease in income over feed cost as  milk production is expected to be lower. 

Reference: 

L. Steyn, R. Meeske & C.W. Cruywagen, 2017. Replacing maize grain with dried citrus pulp in a concentrate feed for Jersey cows grazing ryegrass pasture. S.Afr. J. Anim. Sci. 47, 553-564.