- The research presented in this thesis was designed to evaluate
the effects of feeding alfalfa hays from the Klamath Basin of Oregon
in practical dairy rations on milk fat production in high-producing
Holstein cows. Thirty-two second lactation or older animals estimated
to be capable of producing at least 70 lbs of milk daily were utilized
in a 4 X 4 latin square experiment with eight replications. Four
rations based upon four different lots of hay, ranging from 15.2 to
22.0% crude protein (CP), from 29.9 to 35.1% acid detergent fiber (ADF)
and from 109 to 132 in Relative Feed Value, were fed during four periods,
each lasting about 28 days. Rations were formulated to be comparable
in caloric and nitrogen content, and all consisted (as a percent of
ration dry matter) of 50% concentrate, 30% chopped alfalfa and 20% corn
silage, fed as a mixed, complete ration. A digestibility study was
also carried out involving four steers fed the four alfalfa hays only.
The digestibility trial showed that there were no significant
differences among the four alfalfa hays in feed intake, % digestible
dry matter, % digestible ADF and % digestible CP.
In the production trial, no differences were seen in feed
intake or persistency, and body weight changes were significantly
different only for periods. Both daily 4% fat-corrected milk (FCM)
and milk fat percentage were observed to have highly significant
differences for all sources of variation except treatments. Treatment
means for rations 1 through 4 for 4% FCM were 48.88, 48.02, 48.38 and
48.24 lbs, respectively, and those for percent milk fat were 3.13,
3.12, 3.05 and 3.01, respectively. Differences in other sources of
variation for these two measurements were attributed to variation
among cows and stage of lactation effects.
Important changes were noted in the relative proportions of
volatile fatty acids in the rumen. While there were no significant
changes in rumen acetate concentration, highly significant differences
in propionate content were seen for all sources of variation. Treatment
means for rations 1 to 4 were 18.14, 17.56, 19.44 and 23.03 pmoles
/ml of rumen fluid. This response was reflected also in highly
significant differences in ruminal acetate:propionate (A:P) ratios.
Means here for rations 1 through It were 2.82, 3.00, 2.36 and 2.23,
respectively. Correlation coefficients were determined for A:P ratios
and several hay and ration characteristics, and only that with hay
% NDF was significant. It was concluded that changes in rumen
fermentation typical of milk fat depression occurred which were not
severe enough to actually reduce butterfat levels.
The literature indicates that there may be a relationship between
milk fat synthesis and tissue vitamin B₁₂
status, i.e., that B₁₂-
deficient animals will secrete milk with reduced fat percentage. In
this experiment, serum vitamin B₁₂ levels did not respond significantly
to treatments, nor did fat percentage, the correlation between them
was very low, and there was no indication of vitamin B₁₂
among experimental animals. Our results, therefore, are interpreted
as not being in conflict with the hypothesized relationship.