The influence of pasture crude protein intake on dairy cattle conception efficiency : a thesis presented in partial fulfilment of the requirements for the degree of Master of Philosophy in Veterinary Clinical Sciences at Massey University
Loading...
Date
1992
DOI
Open Access Location
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Massey University
Rights
The Author
Abstract
Excessive dietary rumen degradable protein and high blood
urea nitrogen (BUN) levels are reported to depress conception
efficiency in dairy herds. High protein levels occur in New
Zealand dairy pastures. This study explores the association
of pasture protein and energy levels, and cow BUN, protein
and energy measures with conception efficiency in dairy cows
in the Manawatu region of New Zealand.
A survey study was conducted on 10 dairy farms on which
samples of blood and vaginal mucus were collected from 745
cows within 2 hours before artificial insemination. Blood was
analyzed for BUN, serum albumin (ALB), glucose (GLUC), Bhydroxybutyrates
(BOHB) and non-esterified fatty acids (NEFA)
while vaginal mucus was analyzed for urea nitrogen content
(MUN). Pasture samples were collected weekly during the
animal sampling period and analyzed for crude protein,
metabolizable energy and dry matter content. Reproductive
records, including results of pregnancy diagnosis conducted
8 to 15 weeks after services at which samples were collected,
were obtained from the farms and entered into the DairyCHAMP
computer program.
Pasture crude protein levels ranged from 13% to 28%. The
associations between dietary crude protein levels classified
as high, medium and low and weekly conception rates indicated
that as pasture crude protein increased, fertility decreased
(P<0.005) in cows in their fourth or greater lactation. There
was little variation in pasture metabolizable energy content
and no significant association existed with conception rate.
The association of the probability of conception with BUN and
MUN, and blood levels of ALB, GLUC, BOHB and NEFA when tested
by logistic regression analysis, revealed a significantnegative association between BUN and fertility (P<0.005). MUN
was positively associated with the probability of conception
(P<0.05).
Dietary crude protein from pasture and BUN had a similar
negative influence on fertility in pastured cattle as was
observed in heavily supplemented or fully fed cattle in the
northern hemisphere.
Description
Keywords
Dairy Cattle, Fertility, Reproduction