The possible dilemma of feeding concentrates on pasture.

Milk yield of dairy cows is influenced by genetic merit of the cow, its age, days in milk, daily feed intake, feed quality and body condition score. Milk yield in South Africa is much higher today than two decades ago since we produce 54% more with 24% less cows. As milk yield per se is highly correlated with profit, the push towards higher yields is also noticeable in pasture based systems. For this reason and because of the inadequate nutritive value of forages in comparison to the feeding requirements of the cow, feeding a concentrate mixture during or after milking has become standard practice in many pasture based systems. The question however, is what is the optimum concentrate feeding level defined both in terms of optimum performance and costs.

As expected, research has shown a positive effect on milk yield by feeding more concentrates per day. However, the feed cost of concentrates (Rand/kg) is generally 2-3 times higher than that of forages like cultivated pastures, oats hay or oat silage, maize silage and lucerne hay. Also, concentrates generally have an add-on or replacement effect. For example, on high quality forages such as cultivated pastures, concentrate feeding may replace part of the forage. The replacement effect would also affect the stocking rate on pastures. In South Africa, little research has been conducted on the effect of concentrate feeding level on milk yield, milk composition, gross margins, and stocking rate and milk yield per ha of dairy cows. Therefore the author cited below also consulted some international studies.   

Two studies conducted in South Africa in the seventies and eighties were cited. In the one study the effect of feeding concentrates on the milk yield of Jersey cows on kikuyu pasture was investigated. Concentrate was allocated based on the daily milk yield, i.e. at 0, 0.25, and 0.45 kg concentrate/kg of milk produced. This resulted in cows receiving, on average over the lactation period, 0, 4.2 and 8.4 kg concentrates per cow per day. The results showed that milk yield increased with concentrate feeding levels, being 3639, 4568 and 5003 kg, respectively. Milk fat percentage decreased from 5.09 to 4.81% whereas milk protein percentage increased from 4.14 to 4.29%. The response in milk yield due to feeding 4.2 kg concentrates vs. 0 kg concentrates per day was 0.723 kg per kg concentrate. The response when feeding 8.4 vs. 4.2 kg/day was only 0.354 kg milk per kg concentrate. The response in milk yield of cows at the 8.4 kg/day concentrate feeding level in comparison to no concentrate feeding level was 0.543 kg milk/kg concentrate.

In the second study, the effect of concentrate feeding level on the milk yield of Jersey cows was determined using a step-rate concentrate feeding system. Cows were fed concentrates at no, low, medium and high levels comprising 0, 3, 6 and 9 kg/cow/day from day 1 to 150 days in milk and thereafter 0, 1.5, 3.0 and 4.5 kg/cow/day to the end of the lactation period. The 4% fat corrected milk (FCM) yield was 3741, 4645, 4868, and 5282 kg/lactation, respectively. The milk yield response relative to the zero concentrate feeding level was 1.34, 0.83, and 0.76 kg of 4% FCM for each kg of concentrate fed at the low, medium, and high level of concentrate feeding level. The milk composition and live weight of the cows were not affected by concentrate feeding level, whereas calving interval increased at the higher concentrate levels. The condition score of the cows improved as the level of concentrate feeding increased.

In a USA study, the effect of increasing concentrate feeding levels on the milk yield of Holstein cows grazing ryegrass-clover pasture over two seasons was investigated. The results showed that milk, fat and protein yield increased in a quadratic way (reaching a plateau) at concentrate feeding levels higher than about 6 kg/cow/day. A regression equation indicated that pasture alone would support a milk yield of 20.4 kg/day and that the increase in milk yield diminishes with each increase in the amount of concentrates fed.

Thus, both the local studies as well as the USA study showed the typical response of diminishing marginal returns with regards to concentrate feeding. This obviously will affect gross margins. The author calculated that at a milk yield response of 0.543 kg milk/kg of concentrates fed, feeding concentrates would only be economically viable when the concentrate to milk price ratio is less than 0.543 of the price of milk. Thus, based on the results in the studies discussed, the implication is that when milk prices are low, concentrate feeding levels should be decreased.

The effect of concentrate supplementation on stocking rate was also studied in the USA experiment. It is expected that concentrate supplementation will affect stocking rate because of its replacement effect on forages.  A higher stocking rate should be possible. The amount of pasture substituted was estimated as follows:

Substitution rate of pasture (SR) = 0.093 x kg of concentrate fed per cow/day.

By applying this substitution rate estimation, milk income per ha increased by 10.3, 11.0 and 11.6% at concentrate feeding levels of 4.1, 6.2 and 8.7 kg/cow/day, respectively in Season 1. In Season 2 milk income per ha was different being 3.4, 18.4 and 6.3% at concentrate feeding levels of 4.4, 6.1 and 10.5 kg/cow/day, respectively. It seems that pasture quality was higher in Season 1 than in Season 2; thus season is another variable which should be taken into account.  Although the milk income per ha increased at the higher concentrate feeding levels, the response differences were small, i.e. 11.0 vs. 10.3% at concentrate feeding levels of 6.2 and 4.1 concentrates per day, respectively, and even lower in the second season. Therefore, by feeding more concentrates per cow per day will increase the feeding cost requiring a higher break-even production point. Higher stocking rates increase the risk for a pasture-based system because of possible seasonal droughts. For this reason it seems that dairy farmers will rather maintain a medium stocking rate while feeding concentrates at a higher level. However this will result in an under-utilization of pasture which increases feeding costs.  Thus, farmers need to manage this carefully.

Reference:

C.J.C. Muller, 2019. The effect of concentrate feeding levels on milk yield. In: Agrikultuur, 2019.