TITLE:
Metabolic Adaptations Due to the Inclusion of Pasture in the Diet of Dairy Cows Fed Total Mixed Ration during Early Lactation
AUTHORS:
Ana Laura Astessiano, Ana Meikle, Pablo Chilibroste, Diego Antonio Mattiauda, M. Fajardo, Mariana Carriquiry
KEYWORDS:
Turnout to Pasture, Hepatic Expression, Dairy Cattle
JOURNAL NAME:
Open Journal of Animal Sciences,
Vol.7 No.2,
April
19,
2017
ABSTRACT: The aim of this study was to evaluate the metabolic
adaptations due to the inclusion of pasture in the diet of dairy cows fed on a total mixed ration
(TMR) ad libitum during early lactation. Multiparous cows (n=18) were
used in a randomized complete block design and were randomly assigned according
to parity, BW and BCS to one of two feeding strategies from calving to 60 DIM:
1) cows fed TMR ad libitum (without access to pasture; 100% TMR) and 2) cows fed on a mixed system with pasture
grazing (6 h of access to paddock in one grazing session, 8:00 to 14:00 h) and
supplemented with 50% of ad libitum TMR (Pasture Group, PG). At
61DIM, TMR fed cows were assigned without an adjustment period to a similar
feeding and management routine than PG group (Post-TMR), while PG cows remained in their original
routine throughout the experiment. Thus, at 61DIM and thereafter, both, PG and
Post-TMR cows grazed a
second-year pasture and were supplemented with 50% TMR (DM basis). Milk production
was determined daily until 80 DIM, and cow BCS and BW were registered and blood samples and liver
biopsies were obtained one week before and one week after dietary change (-1 to +1 wk; +55 and +69 DIM). Milk yield, BW and BCS
did not differ between treatments but decreased or tended to decreased from -1 to +1 wk only in Post-TMR cows. Serum IGF-1 tended to
increase in Post-TMR cows. Hepatic expression of IGFBP5 and IGFBP6 mRNA, were greater
while IGF1 and IGFBP3 mRNA tended to be greater for Post-TMR than PG cows. Hepatic expression
of IGF1, IGFBP5 and IGFBP6 mRNA increased from -1 to +1 wk only in Post-TMR cows. Expression of ACADVL and PDH1A mRNA had a 2-fold increase in both groups from
wks -1 to +1. The results confirm that changes in feeding
strategy without an adaptation period modified animal metabolism. The inclusion
of grazing to cows that were fed TMR during early lactation, increased IGF-1
concentrations and modified hepatic expression of genes related with IGF system
and fatty acid metabolism indicating redistribution of nutrients and energy
towards maintenance requirements (increased due to walking and grazing
activity) in detriment of milk production.