Optimal Grazing Strategy for Dairy Cows

Grazing may be a cheap and high quality feed to dairy cows and grazing may provide good animal welfare. However, there is a requirement for either supplementation with concentrates or better grazing systems to sustain high yielding dairy cows on pasture. Pasture allocation to ensure sufficient forage with high quality is difficult, and more knowledge is needed. We conducted six grazing trials with dairy cows. Two trials were conducted at the Animal Production Experimental Centre at Ås in 2014, one (I) experiment early summer (Early) and the other (II) late summer (Late). The four other trials (III, IV, V and VI) were run at Norwegian Centre for Organic Agriculture, Tingvoll, in 2015 (III and IV) and 2016 (V and VI). Here we also run the trials early (III and V) and late (IV and VI). The research questions in all trials were to test if pasture allocation in rotational grazing affects herbage feed quality, herbage intake, and milk production and composition and feed utilization. The hypothesis was that cows allocated to fresh grass daily have access to higher herbage quality and thereby produce more milk and with better feed utilization than cows allocated to an area that covers the requirement for several days. In trials I and II, the following treatments were applied: 7D where cows received weekly allowance at once, S1 where cows received 1/7 of 7D allowance, and S2, where cows grazed like S1 but had also access to the previously grazed part of the paddock. In trials III-VI, we applied the treatments 7D and S2. Each treatment was replicated twice, and we used four lactating dairy cows in each replicate, altogether eight cows per treatment. Trials I-III were run for three weeks, where most of the measurements were done in the last week. Trials IV-VI were run for two weeks, with the same measurements in the last week as the last week of trials I-III. The herbage allowance were planned to be the same in all treatments and was approximately 20 kg dry matter per cow and day. Milk production was recorded at every milking, milk samples were taken regularly and cow live weight were measured at several occasions during the course of the trials. Herbage samples were taken frequently to analyse the botanical composition and to determine the chemical composition and feed quality. Enteric methane production was measured by using the SF6 technique in the trials conducted at Ås. The cows were supplied with a nose-band sensor to observe the eating and rumination activity in both trials at ÅS and in trials V and VI at Tingvoll to test if pasture allocation method affected the grazing behaviour. The herbage chemical composition and feed quality changed during the course of the trials. Generally, the crude protein content, organic matter digestibility and the net energy of lactation decreased while the fibre content increased. However, the effect of allocation method was minor. The changes in herbage quality affected probably the milk production and composition, because both production and milk protein content decrease in all trials. In the trials conducted at Tingvoll, the declining milk yield was stronger in cows that was allocated to new pasture weekly (7D) than in cows that received new strip daily (S2). Milk content of urea was in general low in all trials, and the content decreased during the experimental period. In cows that received weekly allowance at once (7D), the milk urea content was higher in the beginning of the measurement week and declined more than in milk from cows allocated to fresh grass daily. The live weight decreased during the trial periods in cows on treatment 7D, while the cows on S2 maintained their live weight in the trials conducted at Tingvoll. The same effect of pasture allocation on cow live weight was also observed at Ås in ?Late? season, no live weight change in cows that received new grass daily (S1 and S2) and a decrease in cows on 7D. The average total production and intensity of enteric methane were 290 g/d and 12 g/kg milk, but there was no effect of pasture allocation method. Pasture allocation affected the grazing behaviour. Cows that received weekly allowance at once (7D), commenced grazing earlier in the morning than cows that daily got new grass (S1 and S2). Those who received new grass daily spent more time grazing between the milkings at daytime than cows on 7D. Even though we could not observe any effect of grazing treatment on herbage feed quality, the cows allocated to new grass daily (S1 and S2) must grazed herbage of higher quality or had higher herbage intake than those that received new grass every seventh day. This is because the cows allocated to new grass daily maintained their live weight and because the decline in milk yield was lower.

Dairy cow milk production on fresh grass may be cheaper than on conserved forages as grazed forage is the cheapest source of nutrients. However, with grazing dairy cows the supply of protein often is asynchronous to the supply of energy available to rumen microbes and a substantial amount excess nitrogen (N) is excreted in the urine. This low efficiency of N utilization by grazing cows comes with an associated cost of nutrient loss, dairy herd health/fertility through elevated plasma urea, and environment al pollution from the grazed land. Furthermore, differences in the quality of grazed forage may affect milk yield, quality and the extent of gross energy lost as enteric methane (CH4), a strong greenhouse gas (GHG). Decreasing this emission without advers ely affecting animal productivity is desirable both as a strategy to reduce GHG emissions and as a means of improving feed conversion efficiency. The extent to which grazing management can influence N efficiency and CH4 emissions is not known under Norweg ian conditions. To this effect, we plan to investigate the consequences of three different pasture allocation techniques to lactating dairy cows at two different locations within Norway with the following hypotheses and objectives: Balancing nutrient inta ke by dairy cows from grazed pasture through sound grazing management would minimize nutrient loss (e.g. N), improve milk yield and quality and reduce GHG emission. By inference, this will contribute towards improved farm income, sustainable production wi th less harmful effect on environment.