MILKING TWICE DAILY IN THE PRESENCE OF A COW’S OWN CALF FAILS TO PROLONG POSTPARTUM ANESTRUS

Six treatment s were initiated approximately 15 days after calving: 1) calf was weaned permanently from its dam (calf weaned; CW); 2) calf was present continuously with its dam but contact with the udder was prohibited (calf restricted; CR); 3) calf was p resent continuously with its dam ( calf present; CP); 4) CR dam was suckled twice daily by her own calf (CR+S2×); 5) CW dam was milked twice daily (CW+M2×); 6) CR dam wa s milked twice daily (CR+ M2×). During the 4-week treatment period, cows in the CR+M2× treatment had twofold greater yield mi l k and milk components than CW+M2× cows. After completing treatments , calves were returned to their dams and allowed to s u ckle ad libitum. At the time when suckling was reestablished, milk yield was greatest in CP cows, followed by CR+S2×, CR+M2× , and CW+M2× cows, respectively. Although, lactation in CW an d CR cows ceased, it was reinitiated after 1 week of renewed suckling , and increased further by 5 weeks. Cows milked twice daily (CR+M2× and CW+M2×) h ad their first postpartum ovulation about 2 weeks after weaning, similar to cows not milked or suckled (CW and CR). In contrast, cows suckled by their calves either twice daily (CR+S2×) or ad libitum (CP) first ovulated about 5 weeks after initiation of treatments. We concluded that milk removal by suckling, but not mechanically by milking 2× daily, is essential to prolong postpartum anestrus. Furthermore, suckling limited to 2× daily prolonged postpartu m anestrus as much as ad libitum suckling.


Summary
Six treatment s were initiated approximately 15 days after calving: 1) calf was weaned permanently from its dam (calf weaned; CW); 2) calf was present continuously with its dam but contact with the udder was prohibited (calf restricted; CR); 3) calf was p resent continuously with its dam (calf present; CP); 4) CR dam was suckled twice daily by her own calf (CR+S2×); 5) CW dam was milked twice daily (CW+M2×); 6) CR dam wa s milked twice daily (CR+ M2×).During the 4-week treatment period , cows in the CR+M2× treatment had twofold greater yield mi l k and milk components than CW+M2× cows.After completing treatments , calves were returned to their dams and allowed to s uckle ad libitum.At the time when sucklin g was reestablished, milk yield was greatest in CP cows, followed by CR+S2×, CR+M2× , and CW+M2× cows, respectively.Although, lactation in CW an d CR cows ceased, it was reinitiated after 1 week of renewed suckling , and increased further by 5 weeks.Cows milked twice daily (CR+M2× and CW+M2×) h ad their first postpartum ovulation about 2 weeks after weaning, similar to cows not milked or suckled (CW and CR).In contrast, cows suckled by their calves either twice daily (CR+S2×) or ad libitum (CP) first ovulated about 5 weeks after initiation of treatments.We concluded that milk removal by suckling, but not mechanically by milking 2× daily, is essential to prolong postpartum anestrus.Furthermore, suckling limited to 2× daily prolonged postpartu m anestrus as much as ad libitum suckling.

Introduction
Because duration of gesta t ion in cows limits them to one calf crop per year, loss in potential calf gains is attribute d to the failure of cows to conceive during the normal breeding season.That loss can be reduced by shortening the interval to first postpartum estrus.
The cow-calf suckling interaction is a critical component in maintaining anestrus.Previous KSU research showed that cows suckled continuously had longer i ntervals to first estrus than cows whose calves were weaned.Maintainin g cows continuously with their muzzled or nose-plated nonsuckling calves prolonged anestrus as long as when calves were allowed to suckle, because continued calf presence maintained the perception of suckling or milk removal.
Cows nursing foster calves continuously or nursing alien calves continuously in the presence of their own nonsuckling calves (their own calves were present continuously but contact with the udder was prohibited) had intervals to first ovulation similar to those of cows nursing their own calves and longer than those of weaned cows .These observations sugges t that a cow must first recognize the suckling calf to be her own (bonding to her natural born calf or reforming a bond with an alien "foster" calf) before subsequent suckling will prolong anestrus .The present experiment was designed to confirm our earlier report (1996 Cattlemen's Day; KAES Report of Progress 756:22 ) that milking a cow 2× daily in the presence of her own udder-restricted calf would prolong the postpartum interval to first ovulation.An additional objective was to determine to what extent lactation could be reestablishe d after cows were neither suckled nor milked for 4 weeks, followed by renewed ad libitum suckling by their own calf.

Experimental Procedures
Crossbred (Angus × Hereford) cow-calf pairs were used in two replicates following calvings during the spring of 1995 and 1996.Cows were assigned randomly t o six treatments, 15 days after calving: 1) calf was weaned permanentl y from its dam (calf weaned; CW; n=9); 2) calf was present continuously with its dam but contact with the udder was prohibited (calf restricted; CR; n=9); 3) calf was present continuousl y with its dam (calf present; CP; n=9); 4) CR plus dam was suckled twice daily by her own calf (calf restricted + suckled; CR+S2 ×; n=8); 5) CW plus dam was milked twice daily (calf weaned + milked; CW+M2×; n=9); 6) CR plus dam was milked twice daily (calf restricted + milked; CR+M2×; n=9).Cows remained on treatment s for 4 weeks and then were reintroduced to their calves and allowe d to nurse them continuously.Daily blood samples were collected from cows to determin e their first increase in serum progesterone after the initiation of treatments.Ovula tion occurred 1 to 2 days before serum progesteron e exceeded .5 ng/ml for at least 2 days.
Cows were fed individually to meet or exceed NRC recommendations, and intakes were adjusted weekly according to individual body weight and condition.The CW and CR cows were fed as dry second-trimester, pregnant , beef cows and the CP, CR+S2×, CW+M2× , and CR+M2× cows were fed as superio r milk producers.Restricted calves in the CR and CR+M2× treatment were fed a whole-milk replacer twice daily.
Milk production was recorded daily and milk samples were collected weekly to assess contents of fat, protein, lactose, and solids-notfat (SNF) and somatic cell counts (SCC) in the CW+M2 × and CR+M2× treatments.Before and 1 and 5 weeks after reintroducing cows to their calves and suckling ad libitum, 24-hour milk production (two milkings during 24 hours after receiving 40 IU of oxytocin) and fat, prote in, lactose, SNF, and SCC in milk were measured.

Results and Discussion
Average daily milk production characteristics of CW+M2× and CR+M2× cows during the 4-week treatment p eriod are shown in Table 1.Percentage of milk components was similar between treatments, but daily yields of fat, protein, lactose, and SNF in milk were greater (P<.05 ) in CR+M2× cows than in CW+M2× cows.In addition, average daily milk production throughout the 4 -week treatment period was 15.8 lb for CR+M2× compared to 8.4 lb for CW+ M2× cows.
Therefore, the nonsuckling presence of a cow ' s calf is a critical componen t in maintaining milk production in milked beef cows.
Milk yield and SNF for all cow s at the initial reestablishment of sucklin g (0 weeks) and 1 and 5 weeks later are shown in Figure 1.At the time that suckling was reestablished, CP cows had the greatest milk yield, followed by CR+S2×, CR+M2×, and CW + M2×, respectively.
Because CW and CR cows were not suckle d during the 4-week treatment period, they were no longe r lactating.However, after 1 week of renewed suckling, lactation in both groups was reinitiated.After 5 weeks of suckling, milk producti on had increased further, but not to the extent of those cows whose lactation was not interrupted.
Percentage s of milk fat, milk protein, milk lactose, a nd milk SNF before renewed suckling were les s in CW and CR cows than in the other four treatments, but after 1 week of suckling, milk composition was restored to normal percentages .Therefore, although those cows were neither suckled nor milked for 4 weeks, when suckling was reestablished, they reinitiate d sufficient lactation to support a growing calf.