Physical and economic performance of dairy cows managed within contrasting grassland-based milk production systems over 3 successive lactations.

Discipline: performance; Keywords: dairy cattle, fully housed, Jersey crossbreds, grassland systems.

A diverse range of grassland-based milk production systems are practiced on dairy farms in many parts of the world, with slight differences also seen in South Africa. Systems may differ in relation to the proportion of grazed grass, conserved forages and concentrates in diet, calving season, duration of housing, cow genotype, and performance levels. The study of Dr C P Ferris and colleagues summarized here was conducted to examine performance within such diverse grassland-based systems of milk production under experimental conditions. The results were published in the Journal of Dairy Science, Volume 105 of 2022, page 3153 to 3175. The title of the paper is: Physical and economic performance of dairy cows managed within contrasting grassland-based milk production systems over 3 successive lactations.

In the study four milk production systems over three successive lactations and 20 cows per system during each lactation, were investigated. With winter calving-fully housed (WC-FH), Holstein cows were housed for the entire lactation and offered a complete diet consisting of grass silage, maize silage, and concentrates [approximately 50% forage on a dry matter (DM) basis]. With winter calving-conventional (WC-Con), Holstein cows were housed and offered the same diet from calving until turnout in early spring as offered with WC-FH, and thereafter cows were given access to grazing and supplemented with 5.0 kg of concentrate per cow daily. Two spring-calving systems were examined, the former involving Holstein cows (SC-H) and the latter Jersey × Holstein crossbred cows (SC-J×H). Cows on these systems were offered a grass silage-concentrate mix (70% forage on a DM basis) until turnout at the end of winter, and thereafter the cows were given access to grazing supplemented with 1.0 kg of concentrate per cow per day.

The contributions of concentrates (3080, 2175, 722 and 760 kg of DM per cow per lactation), conserved forages (3199, 1556, 1053 and 1066 kg of DM per cow per lactation) and grazed grass (0, 2041, 2788 and 2692 kg of DM per cow per lactation) to total DM intake (6362, 5763, 4563 and 4473 kg of DM per cow per lactation) with WC-FH, WC-Con, SC-H and SC-J×H, respectively, varied considerably. Similarly, milk yield (9333, 8443, 6464 and 6049 kg per cow per lactation), milk fat content (4.49, 4.33, 4.28 and 4.90%), and milk protein content (3.46, 3.49, 3.36 and 3.63%) differed between systems (WC-FH, WC-Con, SC-H and SC-J×H, respectively). The higher milk yields with the WC systems reflect the greater concentrate inputs with these systems, whereas the greater milk fat and protein content with SC-J×H reflect the use of Jersey crossbred cows.

Crossbred cows on SC-J×H produced a similar yield of milk solids as Holstein cows on SC-H. Cows on WC-FH ended the lactation with a greater body weight (BW) and body condition score than cows on any other treatment. While Jersey crossbred cows on SC-J×H had a lower BW than Holstein cows on SC-H, cows on these two systems were not different for any of the other BW, body condition score, or blood metabolite parameters examined. Cows on WC-FH had a greater interval from calving to conception, a greater mastitis incidence, and a greater locomotion score than cows on the spring calving systems.

Whole-system stocking rates and annual milk outputs were calculated as 2.99, 2.62, 2.48 and 2.50 cows per ha, and 25706, 20822, 15289 and 14564 kg of milk per ha, with each of WC-FH, WC-Con, SC-H, and SC-J×H, respectively. Gross margin per cow was highest with WC-Con, whereas gross margin per hectare was highest with WC-FH, and gross margin per kilogram of milk was highest with SC-J×H.

The results of the study demonstrated that diverse grassland-based milk production systems are associated with very different levels of performance when examined per cow and per hectare, which maybe would not have been expected.