EFFECT OF MAIZE PARTICLE SIZE ON STARCH FERMENTABILITY AND LACTATION PERFORMANCE OF DAIRY COWS.

During the transition period (three weeks prior to three weeks after calving), dairy cows experience a period of considerable increase in energy demand coupled with a dramatic reduction in dry matter intake, leading to an unavoidable negative energy balance (NEB), which might cause metabolic and health problems, reduction in milk production as well as in reproductive performance. The site of starch digestion can modulate the negative effects associated with increased rumen starch fermentation such as feed intake, and the occurrence of problems encountered by transition cows. For instance, when the site of starch digestion is shifted post-ruminally, end products of digestion absorbed post-ruminally will not stimulate liver oxidation to the same extent as propionate from the rumen and therefore will not lower feed intake to the same extent. Thus, if rations are fed that partly shift the site of starch digestion from the rumen to the small intestine, some of the nutritional shortcomings associated with meeting the nutrient needs of transition cows may be mediated. One way of shifting part of the digestion post-ruminally is to alter the particle size of the grain source of the diet. The objective of the study cited below therefore was to evaluate the effects of starch fermentability by varying the maize grain particle size of the diet fed during the early post-partum period on feeding behaviour, dry matter intake (DMI), lactation performance and metabolism. The hypothesis was that diets with coarsely ground maize would reduce fermentation of starch in the rumen, hence the production of propionate, thereby limiting the reduction of DMI and possibly improving lactation performance of fresh cows compared with diets with finely ground maize, which are highly fermentable in the rumen.

A total of 117 Jersey cows were used in a randomized block design. Treatment diets were fed as a total mixed ration (TMR) from calving to 30 days post-calving and formulated to contain 28 % of starch, with varying particle size of ground maize (3mm or 6 mm screen sieve) as the primary starch source. Throughout the experiment DMI, milk yield and body weight were measured daily, and milk composition, body condition score (BCS) and blood metabolites were measured weekly.

Feeding coarsely ground maize increased DMI (17.1 vs. 16.1 kg per day) and milk yield (21.7 vs. 20.4 kg per day) during the early post-calving period compared to finely ground maize. Maize particle size did not affect eating time, rumination time, milk protein yield, Energy Corrected Milk, 3.5 % FCM and MUN. Milk lactose was increased by coarsely ground maize compared to finely ground maize (4.70 vs. 4.61 %). Fat percentage tended to be greater (5.57 vs. 5.27%) in the finely ground maize diet, but milk fat yield did not differ (1.13 vs. 1.12 kg). Changes in bodyweight and BCS were greater in cows fed finely ground maize (39.9 vs 32.2 kg and 0.23 vs. 0.14 units, respectively), which reflected also in the concentration of plasma non-esterified fatty acids (NEFA) (0.71 vs. 0.56 mmol per litre). The coarsely ground maize diet decreased the concentration of plasma NEFA, suggesting that these cows were in a better metabolic status as they could reduce the mobilization of body reserves. Blood glucose levels were not affected by the diets. The higher DMI in cows fed the coarsely ground maize diet could possibly be attributed to reduced production of propionate in the rumen, shifting of starch digestion post-ruminally and by the decreased concentration of plasma NEFA.

Bottom line: The results showed that by coarsely grinding the maize portion of the diet, DMI reduction in the immediate post-calving period may be less than in conventional ground maize, which should partially alleviate the negative effects on energy balance, metabolic disturbances during this period and milk yield.

Reference:

M.N.T. Shipandeni, 2019. Effects of starch fermentability of fresh cow diets on feeding behaviour, feed intake, lactation performance and metabolic status of dairy cows in the early postpartum period. Chapter 7 of PhD (Animal Science) thesis: Modulation of starch digestion for productive performance in dairy cows. Faculty of AgriSciences, University of Stellenbosch.