Economics of altering the amount of supplement offered to dairy cows grazing pasture according to nutritional requirements in early lactation

Abstract This study aimed to determine the effect of grouping grazing-based dairy cows by energy and protein requirements and providing differing amounts of supplements on milk production and income over feed costs. The study was part of a larger experiment that also examined the effect of feeding different starch sources during the first 21 DIM and ensuing early lactation period. The experiment used 108 multiparous spring-calving Holstein Friesian cows. Cows were grouped into 3 cohorts of equal numbers based on calving date and then randomly allocated to a Wheat treatment (n = 18) or a Nutritional Grouping treatment (n = 90). Cows in the Wheat treatment remained in that group throughout the experiment, while cows in the Nutritional Grouping treatment were allocated to 1 of 5 groups after 14 DIM. Cows in the Wheat treatment were offered 7 kg DM of wheat grain per day. For cows in the Nutritional Grouping treatment, milk production and composition, BW and BCS data from 7 to 14 DIM were used to estimate individual metabolizable energy and protein requirements. Within each cohort, cows assigned to the Nutritional Grouping treatment were ranked by nutritional requirements with the top 12 categorized as high and the bottom 12 low. Cows were then allocated, based on calving date, to a high Nutritional Group (NGH, n=18) or high Control group (ConH, n=18), or low Nutritional Group (NGL, n=18) and a low Control group (ConL, n=18). These 4 groups were compared in the economic analysis conducted in this study. Cows in the Nutritional Grouping treatment were offered a grain mix in the dairy from 22 to 100 DIM comprising wheat and barley grains and canola meal at 9, 5, or 7 kg DM/cow per d for NGH, NGL and ConH/ConL, respectively. Grazed pasture was provided as the balance of the diet with a target allowance of ~25 kg DM/cow per d (measured to ground level). There was no significant effect of grouping by nutritional requirements on milk yield, milk composition, BW, BCS, or change in BW or BCS. There was also no difference in these parameters between the average of the NGH and NGL groups combined and the average of ConH and ConL. However, NGH cows produced more milk than NGL cows (milk yield; 38. 6 vs 35. 9 kg/cow per d, energy corrected milk yield; 36. 8 vs 34. 1 kg/cow per d). There was no effect of the nutritional grouping strategy on profit (milk income minus the cost of grain mix and pasture). However, NGH cows had the numerically highest profit of 10. 26/cow per d, followed by ConH, NGL and ConL. The average profitability of the NGH and NGL groups combined, was higher than the average profit of ConH and ConL combined, but the difference was small (10. 19 v vs 10. 10/cow per d). Hence, no meaningful economic advantage was determined in this experiment of differentially feeding supplements based on nutritional requirements. Farmers can, therefore, opt for a simpler strategy of providing concentrates at a flat rate to grazing cows without economic penalty during early lactation.