Shortening or omitting the dry period in dairy cows : effects on milk yield, energy balance, metabolic status, and fertility

<p>During early lactation, dairy cows typically experience negative energy balance (EB) caused by the high energy requirement for milk yield, which cannot be met by feed intake. Severity of negative EB has been associated with an increased incidence of metabolic disorders and infectious diseases, subfertility, and increased culling rates. Shortening or omitting the dry period (DP) and feeding glucogenic diet could possibly improve EB in dairy cows. The objective of this thesis was to study the effects of shortening or omitting the DP on milk yield, energy balance, metabolism, and fertility over two subsequent lactations in dairy cows fed a lipogenic or glucogenic diet during early lactation. In the current study, 167 cows were assigned to three DP lengths (0, 30, or 60 days) and two early lactation diets (glucogenic or lipogenic diet), and cows were planned to have same DP length and diet over two subsequent lactations. In the first lactation after DP length and dietary treatments, shortening or omitting the DP improved EB due to a decreased milk yield in the early lactation compared with a conventional DP of 60 days. Omitting the DP or feeding a glucogenic diet improved metabolic status in early lactation. Moreover, omitting the DP increased the percentage of cows with normal resumption of ovarian cyclicity. Shortening the DP to 30 d did not influence metabolic status and fertility compared with conventional DP in dairy cows. In the first lactation, the cows with a 0-d DP had less milk but similar energy intake, leading to excessive weight gain and, therefore, high body condition score (BCS) at onset of the second lactation after DP length and dietary treatments. In the second lactation, improvement of EB in cows with a 0-d DP was less pronounced than the first lactation, which could be related to the high BCS at onset of lactation and reduced milk yield losses. Shortening or omitting the DP did not influence uterine health status, ovarian activity, and reproductive performance in the second lactation. In second lactation, feeding a glucogenic diet improved metabolic status and shortened the interval from calving to first ovulation compared with a lipogenic diet without affecting EB independent of DP length. Furthermore, shortening or omitting the DP decreased peak yield but did not influence lactation persistency in both lactations after implementation of DP treatment. In conclusion, omitting the DP improved metabolic status and resumption of ovarian activity, which was related to an improved EB in early lactation. Shortening the DP for two subsequent lactations could be achieved for most cows with limited milk yield losses. Independent of DP length, glucogenic diet improved EB and metabolic status compared with lipogenic diet in early lactation.