Project Title: Relationship between milk protein percentage and

• The objective of this study was to gain a better understanding of the relationship between milk protein percentage and reproductive performance. This information could then be used as a basis for future field studies, with a possible view to using milk protein percentage, alone or in combination with other variables, as an indicator of energy status and reproductive function. • In this study, a subset of the InCalf Project database was used and then refined to only include Holstein Friesian cows with between one and five milk production records during the first 120 days of lactation in seasonal-calving herds which carried out artificial insemination (AI) for at least the first six weeks of the mating period. This subset then comprised 8,795 cows in 66 herds. • The mean milk protein percentage for all cows in the first 120 days of lactation was 3.15% (range 2.36 – 4.59). Cows with low milk protein percentage were common in the study herds as 95 % of herds (63 of 66) had some cows with low milk protein concentration (less than 3%). • The mean 3-week submission rate was 19 % lower for cows in the lowest (62.5%) compared to the highest (81.5%) quartile for milk protein percent. The mean 6-week incalf rate was 15% lower for cows in the lowest (52.9%) compared to the highest (67.8%) quartile for milk protei