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Most of the energy in dairy cow concentrates comes from maize, resulting in a dairy ration high in starch. Starch is primarily fermented to propionic and acetic acid, but when the rumen pH drops below 6 some lactic acid is also produced. Below pH 5.8 and especially 5.5, lactic acid begins to accumulate and animals could begin to show signs of sub-clinical rumen acidosis. This is detrimental to pasture dry matter (DM) and fiber (NDF) degradation and leads to a decrease in milk fat and protein content, as well as a decrease in efficiency of energy use. Contrary to starch which is the primary carbohydrate in maize, pectin and sucrose as in citrus pulp are not fermented to lactic acid but rather to butyric and acetic acid, contributing to a more favourable ruminal pH. Thus, if citrus pulp can replace maize in supplements to cows on pasture, it could serve the purpose of supporting an improved rumen environment and, because it is a waste product, could reduce supplementary costs.
The aim therefore in the first study was to determine the effect on rumen activity and health by replacing 100% maize with citrus pulp in a concentrate feed. Six rumen cannulated Jersey cows were randomly allocated to one of two treatments in a two period cross-over design. The treatments were: high maize (75% maize and 0% citrus pulp inclusion) and high citrus pulp (0% maize and 75% citrus pulp inclusion). The cows in both treatments received 6 kg DM of the relevant concentrate per day and were allocated 10 kg DM pasture per day. The ME content of the high maize and high citrus pulp diets was 9.8 and 9.4 MJ per kg DM respectively, the crude protein content 9.8 and 10.1 g per kg DM and the NDF content 151 and 333 g per kg DM, the latter showing the substantial difference in fiber content. The rumen parameters measured included ruminal pH, volatile fatty acid (VFA) content and within-rumen ryegrass DM and NDF degradability.
There was no difference in the diurnal ruminal pH curve between the high maize and high citrus pulp treatments. The average rumen pH over a 24 hour cycle was 6.25 and 6.17 for the high maize and high citrus pulp treatments, respectively. There was also no difference in the time pH went below 6.0 and 5.8 between treatments. Furthermore, there was no difference in VFA and the rate and extent of pasture DM and NDF degradability between treatments.
In conclusion, the replacement of maize with citrus pulp did not change the rumen environment measurably. From a rumen activity and health viewpoint therefore, it is possible to replace 100% of the maize in a dairy concentrate fed to cows grazing ryegrass pasture with citrus pulp. From an economical point of view, the success will depend on the milk yield obtained in relation to the price paid for the citrus pulp.
In the second study, palm kernel expeller (PKE) which is a low-cost, high fibre by-product from the palm-oil industry was evaluated as substitute for maize. The energy (range: 10.5 – 12.0 MJ/kg DM) and crude protein content (range: 14.2 to 19.6% DM) of PKE is comparable to that of corn gluten or rice bran. A positive milk fat response has been reported previously in cows grazing kikuyu pasture when PKE was included up to 30% in a dairy concentrate, without adverse effects on fat corrected milk yield and other milk components. The objective in this study was to determine the effect of partially replacing maize with PKE in the concentrate supplement on rumen fermentation of Jersey cows grazing kikuyu-based pasture during summer.
Eight rumen-cannulated Jersey cows were randomly allocated to four treatments (PKE0, PKE10, PKE20 and PKE30) in a 4x4 Latin square design. The PKE inclusion in the PKE0, PKE10, PKE20 and PKE30 treatment concentrate supplements was 0, 10, 20 and 30%, respectively, replacing part of the maize and soybean oilcake. The nutrient compositions of the supplements were otherwise similar. All cows grazed kikuyu pasture as one group and concentrate was fed at 6 kg per cow per day in the dairy parlour during milking (3 kg per milking). The pasture was allocated at 10 kg DM per cow per day above a height of 30 mm. Cows were offered PKE ad libitum in feed troughs on the pasture for 7 days prior to the study. This was followed by 14 days adaptation to the allocated treatment supplements and a 8 day measurement period. Ruminal pH, ammonia nitrogen and VFA concentrations, and within rumen pasture DM degradability (DMd), NDF degradability (NDFd) as well as rate of NDFd (NDF kd) were determined.
The mean ruminal pH did not differ between treatments and was 6.44, 6.53, 6.52 and 6.50 for cows on the PKE0, 10, 20 and 30 treatments, respectively. However, the daily rumen pH of cows on the PKE0 (100% maize/soybean) treatment was below pH of 6.0 for a longer period at 2.13 compared to respectively 0.13, 0.06 and 0.31 hours per day for cows on the PKE10, 20 and 30 treatments. In terms of VFA fractions (% of total VFA), only iso-butyric and valeric acid differed between treatments, which is not of major concern. Dry matter degradability, NDFd and NDF kd were the lowest for cows on the PKE30 treatment at both the 18 and 30 hour incubation intervals.
In conclusion, it was shown that PKE sustained a favourable ruminal pH and VFA profile up to an inclusion level of 30%. However, the 30% inclusion level resulted in reduced pasture degradability. This could be attributed to a too high fat level in the diet, induced by PKE. In practice then, substitution of maize by palm kernel expeller up to 20% should be effective.
References:
L. Steyn, R. Meeske & C.W. Cruywagen, 2015. Rumen response in Jersey cows grazing ryegrass pasture to two levels of high fibre concentrate supplementation. Proc. of the 48th SASAS Congress, 21-23 September, Empangeni.
J.D.V. van Wyngaard & R. Meeske, 2015. Effect of palm kernel expeller supplementation on rumen fermentation of Jersey cows grazing kikuyu-based pasture. Proc. of the 48th SASAS Congress, 21-23 September, Empangeni.