Milking two or five times daily in the presence of a cow’s own nonsuckling calf fails to prolong postpartum anovulation

Three treatments were initiated at approximately 15 days after calving and continued for 4 weeks: 1) cows were suckled ad libitum by their calves (calf present [CP]); 2) calves were present but nonsuckling 24 hr/day and cows were milked twice daily (CR+2xM); 3) or same as CR+2xM but cows were milked five times daily (CR+5xM). Interval to the first postpartum ovulation was similar between CR+2xM and CR+5xM cows but about 2 weeks less than that in cows suckled ad libitum by their own calves. Cows in the CR+5xM treatment produced more milk than cows in the CR+2xM treatment, whereas only slight differences occurred in the percentages of milk fat, protein, lactose, and solids-not-fat. Prior to initiation of treatments, CR+2x cows yielded more milk than either CR+5xM or CP cows, but by the end of 4 weeks of treatment, milk yields were similar among treatments. We conclude that mechanical milking either two or five times daily in the presence of a cow's own nonsuckling calf fails to prolong postpartum anovulation to the extent of ad libitum suckling. However, increasing milking frequency to 5x daily enhanced milk yield.


Introduction
Reproduction is a major factor limiting efficiency of production in beef cattle enter-

Experimental Procedures
During the spring of 1997, 30 Angus × tactile, and olfactory contacts during milking.Hereford cow-calf pairs were assigned ran-To establish milk production at the onset and domly on day 15 postpartum to three treat-termination of all three treatments, pairs were ments of 10 pairs each; 1) calf was present separated for 8 to 10 hr and cows were continuously with its dam (CP); 2) calves milked after a 40 I.U.injection of oxytocin.were present but nonsuckling 24 hr/day, plus Milk yield was recorded and adjusted to a 24cows were milked twice daily (6:00 AM and hr period.Individual samples also were 6:00 PM) (CR+2×M); and 3) calves were collected for component analysis.present 24 hr/day, plus cows were milked at 6:00 AM, 10:00 AM, 2:00 PM, 6:00 PM, and 10:00 PM) daily (CR+5×M).Cows remained on treatments for 4 weeks, after which calves Average daily milk yields for CR+2×M were allowed to nurse until weaning at 205 and CR+5×M cows during the 4-week treatdays of age.During treatments, daily blood ment period are shown in Figure 1.Average samples were collected from cows for serum daily milk yield was 17% greater (P<.05) for progesterone analysis.Ovulation occurred 1 cows milked 5× daily than for cows milked to 2 days before serum progesterone ex-2× daily.Therefore, increasing the frequency ceeded .5 ng/ml for at least 2 days.
of milk removal enhanced total daily milk Cow-calf pairs were housed individually cows. in pens located in two separate open-front barns.After initiating treatments on day 15 Intervals to the first postpartum increase postpartum and throughout the treatment in serum progesterone (1 to 2 days after period, calves in the CR+2×M and CR+5×M ovulation) are summarized in Table 1.Cows treatments were confined to a hutch within in both CR+2×M and CR+5×M treatments their dam's pen.The hutch permitted head had similar intervals to ovulation, which were and neck contact between cow and calf, but shorter (P < .05)than that for cows in the CP no contact with the udder.Cows were fed treatment.Previously (1997 Cattlemen's individually to meet or exceed NRC recom-Day; KAES Report of Progress 783:99), we mendations for superior milk producers, and demonstrated that milking cows 2× daily in intakes were adjusted weekly according to the presence of their own nonsuckling calves changes in individual body weight and condi-(CR+2×M) failed to prolong postpartum tion.
anovulation to the extent observed in cows suckled 2× daily or ad libitum by their own Cows assigned to the two milking treat-calves.Moreover, increasing the frequency ments were milked in an enclosed restraining of milking from 2× to 5× daily also failed to chute, using a portable milking machine.
prolong postpartum anestrus, unlike the Milk yield was recorded at each milking, and situation in dairy cows.We conclude that weekly samples were collected for measure-milk removal by suckling is essential to ments of fat, protein, lactose, solids-not-fat prolong postpartum anestrus in beef cows.(SNF), and somatic cell count (SCC).During each milking, the cow's own calf was shuttled from its hutch to the chute where cow and calf were permitted visual, audible,

Results and Discussion
yield, which has been observed also in dairy Cows were suckled by their own calf until 4-week treatments were initiated on day 15 postpartum.b Days from initiation of treatments. x,y Means with uncommon superscript letters differ (P < .01).

Figure 1 .
Figure 1.Average Daily Milk Yield in Cows that Were Milked during 4 Weeks Starting 15 Days Postpartum.Cows Were Suckled Ad Libitum by Their Own Calves until Treatments Began.