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Effect of monensin, energy level, and cow body condition on pregnancy rate in nonlactating beef cows
THERIOCENOLOGY EFFECTOF MONENSIN,ENERGYLEVEL, AND COW BODY CONDITION ON PpEGNANCY RATE IN NONLACTATING BEEF COWS' M. F. Smith2, L. D. Shipp, W. N. Songster, and L. ii. Carroll3 Texus AgricultwaZ Experiment Eli LitZy aid Co.',
J. N. Wiltbank
Station, BeeviZle DaZZas 75234
Received for publication:
78102
2128180
Abstract One hundred eighty-two nonlactating cycling Brahman crossbred and Angus cows were used to study the effects of monensin, cow body condition and supplemental energy level on pregnancy rate. The cows were classified as being in either moderate or poor body condition at the start of the experiment and were fed either 9 or 18 Meal of supplemental metabolizable energy/head/day with or without 125 mg of monensin in the ration. Feeding commenced 21 days prior to and throughout a 45-day breeding season. In the monensin treated group ruminal propionic acid levels (molar %) were increased (Pc.01) while acetic and butyric acid levels were lowered (Pe.05) regardless of supplemental energy intake. Pregnancy rate, pregnancy rate at first service, and the percentage of conceptions per estrus were increased (Px.05) when cows were fed 18 Meal of supplemental energy per head per day. Neither cow body conditionnoraddition of monensin to the diet had an effect on the preceding reproductive endpoints. Cows in poor body condition and receiving 18 Meal of supplemental energy per head per day had increased (Px.05) reproductive performance as evidenced by an increase in the pregnancy rate, pregnancy rate at first service, and percentage of conceptions per estrus when compared to the other groups. (Key
Words:
Monensin, Pregnancy Rate, Cow Body Condition, Beef Cows).
Energy Level,
1 Published with the approval of the Director of the Texas Agricultural Experiment Station, Texas A&M University System, as Scientific Series Paper No. 14914. 2 Present Address: Research Center, 3 Eli Lilly
University of Missouri, 160 Animal Science Columbia, Missouri 65211
and Co., Dallas,
TX 75234
4 Monensin was donated by Eli Lilly
AUGUST
1980 VOL.
14 NO. 2
and Co., Greenfield,
IN
91
THERIOGENOLOGY Introduction Increasing the pregnancy rate at first service would result in more cows calving early in the calving season and consequently improve the reproductive performance in beef herds. Monensin is a biologically active feed additive which is produced by streptomyces cinnamonensis and has been reported to increase feed efficiency (2, 12), rate of gain (11, 16), onset of puberty in beef heifers (7), onset of the post-partum estrus (16), and ruminal molar percentage of propionic acid in vitro and -in vivo (10, 12, 13, 16). In a study conducted at thx Station, the pregnancy rate at first service was 51% in 35 cows fed monensin compared to 38% in 28 control animals (P>.OS) (3). Level of nutrition and cow body condition have long been considered important factors affecting reproductive performance in beef cows. Although cow body condition (amount of fat cover over the back and ribs) at calving was reported to affect the onset of estrus, cow body condition at breeding time had no effect on the pregnancy rate at first service (19). The objective of this study was to determine the effect of monensin, energy level, and cow body condition on pregnancy rate in nonlactating, cycling beef cows. Experimental
Procedure
One hundred eighty-two nonlactating Brahman crossbred and Angus cows from 2 to 10 years of age and weighing between 231 and 495 kg were allotted to treatment groups by breed and cow body condition. The cows had calved within 6 months of the experiment and the calves had been weaned 1 to 2 months prior to the start of the experiment. The cows were used in a previous experiment to induce estrus in post-partum cows suckling calves. EStNS was not induced in these cows ; therefore, the calves were weaned so that the cows would cycle. The experiment was a 2 x 2 x 2 factorial arrangement of treatments involving monensin, level of supplemental energy, and cow body condition as outlined in table I. The experiment was conducted from January 3 through March 11th and the rations were fed for 21 days prior to and during the 45-day breeding period. The cows were divided into two groups according to supplemental energy level and were placed'in separate bermudagrass pastures during the experimental period. The supplements contained coastal Bermuda hay (l-00-716), ground milo grain (4-04-444), and guar meal (S-05-687) and were formulated to provide either 18 Meal of metabolizable energy/head/day and 0.6 kg of digestible protein or 9 Meal of metabolizable energy/head/day and 0.37 kg of digestible protein (table II). All of the cows were brought daily into a dry lot and sorted within supplemental energy level into four preassigned groups (approximately 24 cows per group) according to cow body condition (poor or moderate) and ration (monensin or control). Thus the cows were sorted into the 8 groups outlined in table I before they were fed the concentrate portion of the supplement. The cows receiving 9 Meal/head/day of supplemental energy were fed the hay portion of
92
AUGUST 1980 VOL. 14 NO. 2
THERIOCENOLOGY
the ration while in these groups; whereas the cows receiving 18 Meal/head/day of supplemental energy were fed hay together after returning to pasture. The level of hay was decreased by one half at the start of the breeding season due to a hay shortage and additional grain added to the ration in order to maintain the appropriate supplemental energy level in each group. Cows in the monensin group received an average of 125 mg of monensin/head/day in the concentrate portion of the supplement. Rumen samples were obtained from 20 cows at the start of the breeding season and assayed for acetic, butyric, and propionic acid. Cow body condition was subjectively determined at the start of the experiment by one technician. The fat cover over the back and ribs was manually palpated and cows were assigned a body condition score ranging from 1 to 9 indicating the lowest to highest body condition, respectively. Cows having body condition scores of 4 or less were considered in poor body condition whereas cows having body condition scores of 5 or greater were considered in moderate body condition. Estrus detection was conducted twice daily using homosexual activity as an indicator, The cows were artificially inseminated by one of three technicians approximately 12 hr after estrous detection. Cows were randomized so that approximately an equal number in each group were bred by each technician to each bull. Pregnancy diagnosis per rectum was conducted 45-60 days postinsemination. Statistical analysis of the data involved Chi Square Analysis, and Analysis of Variance using Duncans Multiple Range Test to determine differences between means (15). Results
and Discussion
Cow body condition scores ranged from 3 to 7 at the start of the experiment and from 4 to 7 at the end of the experiment. cows receiving 18 Meal/head/day of supplemental energy gained an average of 25 kg and the weight change for cows within the monensin and control groups was similar (P>.O5, table III). Cows receiving 9 Meal/head/day of supplemental energy lost an average of 7 kg during the first half of the breeding season and gained an average of 17 kg during the second half of the breeding season for an overall average weight gain of 10 kilograms. The weight change was similar for cows within the monensin and control groups (P>.OS). The large amount of variation in weight change within groups should be noted (table III). The cows were maintained on pasture and undoubtedly the pasture and supplement intake varied between cows. The group receiving only 9 Meal/head/day of supplemental energy gained from 12 to 22 kg during the second half of the breeding season. The nutrient intake from the pasture probably increased during this period since the pasture was beginning to improve thus increasing energy intake. Regardless of energy level, the cows receiving monensin had higher (P<.O5) propionic acid levels and lower (Pc.05) acetic and butyric acid levels in the ruminal fluid than the control animals; consequently, total volatile fatty acids were similar (table IV).
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1980 VOL.
14 NO. 2
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THERIOGENOLOGY
Level of supplemental energy significantly influenced the pregnancy rate, pregnancy rate at first service, and the percent conceptions per estrus, whereas monensin and cow body condition did not. An increase of 19 percentage units in pregnancy rate (P<.OOS), 19 percentage units in pregnancy rate at first service (Pc.01) and 12 percentage units in conceptions per estrus (Pc.005) were noted in cows receiving 18 Meal/head/day of supplemental energy compared to cows fed 9 Meal/head/day of supplemental energy (table V). Theoretically, the energy available to cows should be increased when they receive monensin. By receiving 9 Meal/head/day of supplemental energy (a deficient amount) a consequential increase in energy should be available to cows receiving monensin. Consequently, the weight gains and reproductive performance limited by low energy intake might be improved. Conversely, no difference between monensin and control groups would be expected in the cows receiving 18 Meal/head/day of supplemental energy since the energy intake would probably be adequate. Weight gains and reproductive end points (pregnancy rate, pregnancy rate at first service, and conceptions/ estrus) were similar for the monensin and control groups that received In fact, all three reproductive 9 Meal/head/day of supplemental energy. end points in the cows receiving 9 Meal/head/day of supplement tended to be higher in the control cows than in the cows receiving monensin (P>.OS, table VI). An important finding of this study was the increase in reproductive performance for cows in poor body condition and receiving a supplement of 18 Meal/head/day. The pregnancy rate after 45 days of breeding was 19 to 33 percentage units higher in the cows in poor body condition receiving 18 Meal of supplemental energy/head/day than in the other three groups (Pc.05, table VII). Similar differences in pregnancy rate at first service (Pc.05) and conceptions per estrus (Pc.05) were noted. The increase in the conception rate of poor body condition cows receiving 18 Meal/head/day of supplemental energy is similar to the results reported in postpartum beef cows receiving 150% of the NRC requirements (21). However, the length of feeding time and/or feed level necessary to obtain an increase in conception rate is unknown Feeding monensin (125 mg per day) did not increase (P>.OS) weight gain, pregnancy rate, pregnancy rate at first service nor the percentage of conceptions per estrus in nonlactating beef cows fed either 9 or 18 Meal/head/day of supplemental energy. Other workers have noted an increase in weight gain with cows receiving roughage rations (16), growing cattle on pasture (8, 11) or growing heifers fed hay (17). In feed lot cattle, no increase in weight gain has been reported, however, feed efficiency has been improved (2, 12). The failure to find a weight change response in this study could be a result of the lower level of monensin fed (125 mg vs 200 mg in The increases in propionic other studies) or the ration composition. acid in the rumen of 32% and 48% are similar to the increases reported by other workers (4, 10, 12, 16, 17). Thus, the 125 mg of monensin fed in this study was as effective at increasing propionic Alternativeacid levels as the 200 mg of monensin fed in other studies. ly, factors other than an increase in propionic acid may be important in increasing weight gain in cows fed monensin. It has been reported
AUGUST 1980 VOL. 14 NO. 2
THERIOGENOLOGY
that the addition of monensin to a roughage ration decreased feed intake and animal performance (9). The rations fed in the present study were different than those in other studies; therefore, no direct comparison could be made. Other workers have reported increased reproductive performance in animals receiving monensin; however, the improvements were in the onset of the postpartum estrus (16) and a decrease in puberal age (7). The endocrine mechanisms regulating the onset of puberty and the onset of estrus may be different than the mechanisms regulating conception even though an improvement in weight gain has been reported to be important in each case (1, 5, 20, 21). The failure of cow body condition to effect the reproductive end points studied here was not unexpected (19). Most cows in poor body condition had achieved moderate body condition by the end of the study which may have been one reason there was no difference in reproductive performance between the two body condition groups. The lower reproductive performance in cows fed 9 Meal/head/day of supplemental energy compared to cows receiving 18 Meal/head/day of supplemental energy is similar to that noted by other workers. Numerous workers have reported that underfeeding prior to and during the breeding season decreases the pregnancy rate in cows and heifers (6, 14, 18). The effect of feeding different energy levels for varying lengths of time on pregnancy rate in beef cows needs to be explored more thoroughly and the hormonal mechanism elucidated.
AUGUST
1980 VOL.
14 NO. 2
9s
THERIOGENOLOGY Literature
Cited
1. Arije, G. F. and J. N. Wiltbank. 1971. in Hereford heifers. J. Anim. Sci.
Age and weight at puberty 33:401.
2. Brown, H. L., L. H. Carroll, N. G. Elliston, H. F. Grueter, J. W. McAskill, R. D. Olson and R. P. Rathmacher. 1974. Field evaluation of monensin for improving feed efficiency in feedlot cattle. Proc. Western Section, ASAS 25:300. beef 3. Burrell, W. C. 1977. The effect of monensin in lactating cows in poor body condition receiving low levels of energy. Ph.D. Dissertation, Texas A&M University, College Station. 4. Dinius, D. A., M. E. Simpson and P. B. Marsh. 1976. Effect of monensin fed with forage on digestion and the ruminal ecosystem of steers. J. Anim. Sci. 42:229. 5. Dunn, T. G., J. E. Ingalls, D. R. Zimmerman and J. N. Wiltbank. 1969. Reproductive performance of 2 year old Hereford and Angus heifers as influenced by pre- and post-calving energy J. Anim. Sci. 29:719. intake. 6. Lamond, D. R. 1969. Sources of variation in reproductive performance in selected herds of beef cattle in north-eastern Australia. Australian Vet. J. 45:50. 7. Moseley, W. M., M. M. McCartor, R. D. Randel. 1977. Effects monensin on growth and reproductive performance of beef J. Anim. Sci. 45:961. heifers.
of
8. Oliver, W. M. 1975. Effect of monensin on gains of steers grazed on Coastal Bermudagrass. J. Anim. Sci. 41:999. 1977. Performance 9. Oltjen, R. R., D. A. Dinius and H. K. Goering. of steers fed crop residues supplemented with nonprotein nitrogen, minerals, protein and monensin. J. Anim. Sci. 45:1442 1976. Effect of 10. Perry, T. W., W. M. Beeson and M. T. Mohler. monensin on beef cattle performance. J. Anim. Sci. 42:761. 11. Potter, E. L., C. 0. Cooley, L. F. Richardson, A. P. Raun and R. P. Rathmacher. 1976. Effect of monensin on performance of cattle fed forage. J. Anim. Sci. 43:665. 12. Raun, A. P., C. 0. Cooley, E. L. Potter, R. P. Rathmacher and 1976. Effect of monensin on feed efficiency L. F. Richardson. of feedlot cattle. J. Anim. Sci. 43~670. 13. Richardson, L. F., A. P. Raun, E. L. Potter, C. 0. Cooley and R. P. Rathmacher. 1976. Effect of monensin on rumen fermentation in vivo. J. Anim. Sci. 43~657. --in vitro and --
96
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1968. Some factors 14. Schilling, P. E. and N. C. England. reproduction in beef cattle. J. Anim. Sci. 27:1363. 1960. Principals 15. Steel, R. G. D. and J. H. Torrie. McGraw-Hill Book Co., New York. of Statistics.
affecting
and Procedures p. 360.
16. Turner, H. A., R. J. Raleigh, and D. C. Young. 1977. Effect of monensin on feed efficiency for maintaining gestation mature cows wintered on meadow hay. J. Anim. Sci. 44:338. 17. Utley, P. R., G. L. Newton, R. J. Ritter, III and W. C. McCormick. 1976. Effects of feeding monensin in combination with zeranol and testosterone-estradiol implants for growing and J. Anim. Sci. 42~754. finishing heifers. 1967. 18. Warnick, A. C., R. C. Kirst, W. C. Burns and M. Koger. Factors influencing pregnancy in beef cows. J. Anim. Sci. 26:231 (Abstr.). 1975. 19. Whitman, R. W., E. E. Remmenga, and J. N. Wiltbank. Weight change, condition and beef cow reproduction. J. Anim. Sci. 41:387 (Abstr.). 20. Wiltbank, J. N., W. W. Rowden, J. E. Ingalls, K. E. Gregory, and R. M. Koch. 1962. Effect of energy level on reproductive phenomena of mature Hereford cows. J. Anim. Sci. 21:219. 21. Wiltbank, J. N., W. W. Rowden, J. E. Ingalls and D. R. Zimmerman. 1964. Influence of postpartum energy level on reproductive performance of Hereford cows restricted in energy intake prior to calving. J. Anim. Sci. 23:1049.
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THERIOGENOLOGY
TABLE I.
EXPERIMENTALDESIGN
Supplemental energy level (Meal ME/hd/day)
Cow body condition Moderate Poor 9 Meal 18 Meal 9 Meal 18 Meal
Treatment Monensin
aa
24
19
22
Control
24
24
22
23
a No. cows/treatment
group
AUGUST 1980 VOL. 14 NO. 2
THERIOGENOLOGY
FJ . M
u-i d
-r . %-I
r-7
d
w-2
2.
In
N
0
d
01
2.
0
hl M
AUGUST
1980 VOL.
14 NO. 2
m
In
0 m
%.
99
THERIOGENOLOGY
TABLE III. COW WEIGHTCHANGES FOR THE 53 DAY PERIODNEARTHE BREEDINGSEASON
Weight change (kg) Before to middle of breeding season (26 days) Supplemental energy 18 Meal o:,-.&/head/day
Middle to end of breeding season (27 days)
Beginning weight (kg)
Monensin Moderate condition Poor condition
(kg)
(kg)
374 -+ 46
11 + 12a
14 + - 7
326 -+ 41
13 -+ 10
14 -+ 8
386 -+ 54
12 + 11
15 -+ 31
340 -+ 43
10 -+ 12
11 + 8
359 -+ 49
-4 -+ 15
12 -+ 14
327 -+ 38
-4 -+ 8
17 -+ 8
368 -+ 36
-14 -+ 8
17 -+ 9
324 -+ 39
.-7 -+ 11
22 -+ 11
Control Moderate condition Poor condition
(kg)
(kg)
Supplemen+ energy 9 Meal of ME/head/day Monensin Moderate condition Poor condition
(kg)
(kg)
Control Moderate condition Poor condition
(kg)
(kg)
a Standard deviations
AUGUST
1980 VOL.
14 NO. 2
THERIOGENOLOGY
m . m +I c-4 .
AUGUST
1980 VOL.
14 NO. 2
d . m +I 00 .
101
Moderate condition Poor condition
c,d
Figures
in the same column having different
superscripts
superscripts
71 69
18 Meal/head/day 9 Meal/head/day
in the same column having different
50 47
80a 61b
Monensin Control
Figures
63c 44d
70 70
Treatment
a,b
50 57
Pregnancy rate (%)
are different
are different
(Pc.01).
(P<;bD5).
49 54
58a 4tjb
50 54
Conception per estrus (%I
EFFECTOF MONENSIN,ENERGYLEVEL, AND COWBODYCONDITION ON REPRODUCTIVE ENDPOINTS
Pregnancy rate at 1st service ("a)
TABLE V.
THERIOGENOLOGY
TABLE VI.
EFFECTOF MONENSINON PREGNANCY RATE, PREGNANCY RATEAT FIRST SERVICE, AND CONCEPTIONS PER ESTRUSIN COWSFED EITHER 9 MCAL OR 18 MCAL OF SUPPLEMENTAL ENERGYPER HEADPER DAY
Treatment
9 Meal/head/day
Energy level (%) lb'Mcal/head/day
pregnancy rate 45day
period
Monensin
5ga
a2b
Control
63
78
Pregnancy rate
(first
service)
Monensin
37a
62b
Control
50
64
Conceptions
per estrus
Wnensin
43
56
Control
48
60
a,b
Figures in the same row having different different (Pc.05).
AUGUST
1980 VOL.
14 NO. 2
(%)
superscripts
are
103
Moderate
18 Meal/head/day
73b
96a
in same column having different
Poor
18 I&al/head/day
Figures
Moderate
g.Mcal/head/day
"b'c
Poor
Cow body condition
superscripts
Pregnancy rate 45 days 01
are different
54ab
7za
Pregnancy rate (1st service) e-1
(Pc.05).
50b
7oa
Conceptions per estrus 0)
EFFECTOF SUPPLEMENTAL ENERGYLEVEL AND COWBODYCONDITION ON REPRODUCTIVE ENDPOINTS
9 Meal/head/day
Supplemental energy level
TABLEVII.
J. N. Wiltbank
Station, BeeviZle DaZZas 75234
Received for publication:
78102
2128180
Abstract One hundred eighty-two nonlactating cycling Brahman crossbred and Angus cows were used to study the effects of monensin, cow body condition and supplemental energy level on pregnancy rate. The cows were classified as being in either moderate or poor body condition at the start of the experiment and were fed either 9 or 18 Meal of supplemental metabolizable energy/head/day with or without 125 mg of monensin in the ration. Feeding commenced 21 days prior to and throughout a 45-day breeding season. In the monensin treated group ruminal propionic acid levels (molar %) were increased (Pc.01) while acetic and butyric acid levels were lowered (Pe.05) regardless of supplemental energy intake. Pregnancy rate, pregnancy rate at first service, and the percentage of conceptions per estrus were increased (Px.05) when cows were fed 18 Meal of supplemental energy per head per day. Neither cow body conditionnoraddition of monensin to the diet had an effect on the preceding reproductive endpoints. Cows in poor body condition and receiving 18 Meal of supplemental energy per head per day had increased (Px.05) reproductive performance as evidenced by an increase in the pregnancy rate, pregnancy rate at first service, and percentage of conceptions per estrus when compared to the other groups. (Key
Words:
Monensin, Pregnancy Rate, Cow Body Condition, Beef Cows).
Energy Level,
1 Published with the approval of the Director of the Texas Agricultural Experiment Station, Texas A&M University System, as Scientific Series Paper No. 14914. 2 Present Address: Research Center, 3 Eli Lilly
University of Missouri, 160 Animal Science Columbia, Missouri 65211
and Co., Dallas,
TX 75234
4 Monensin was donated by Eli Lilly
AUGUST
1980 VOL.
14 NO. 2
and Co., Greenfield,
IN
91
THERIOGENOLOGY Introduction Increasing the pregnancy rate at first service would result in more cows calving early in the calving season and consequently improve the reproductive performance in beef herds. Monensin is a biologically active feed additive which is produced by streptomyces cinnamonensis and has been reported to increase feed efficiency (2, 12), rate of gain (11, 16), onset of puberty in beef heifers (7), onset of the post-partum estrus (16), and ruminal molar percentage of propionic acid in vitro and -in vivo (10, 12, 13, 16). In a study conducted at thx Station, the pregnancy rate at first service was 51% in 35 cows fed monensin compared to 38% in 28 control animals (P>.OS) (3). Level of nutrition and cow body condition have long been considered important factors affecting reproductive performance in beef cows. Although cow body condition (amount of fat cover over the back and ribs) at calving was reported to affect the onset of estrus, cow body condition at breeding time had no effect on the pregnancy rate at first service (19). The objective of this study was to determine the effect of monensin, energy level, and cow body condition on pregnancy rate in nonlactating, cycling beef cows. Experimental
Procedure
One hundred eighty-two nonlactating Brahman crossbred and Angus cows from 2 to 10 years of age and weighing between 231 and 495 kg were allotted to treatment groups by breed and cow body condition. The cows had calved within 6 months of the experiment and the calves had been weaned 1 to 2 months prior to the start of the experiment. The cows were used in a previous experiment to induce estrus in post-partum cows suckling calves. EStNS was not induced in these cows ; therefore, the calves were weaned so that the cows would cycle. The experiment was a 2 x 2 x 2 factorial arrangement of treatments involving monensin, level of supplemental energy, and cow body condition as outlined in table I. The experiment was conducted from January 3 through March 11th and the rations were fed for 21 days prior to and during the 45-day breeding period. The cows were divided into two groups according to supplemental energy level and were placed'in separate bermudagrass pastures during the experimental period. The supplements contained coastal Bermuda hay (l-00-716), ground milo grain (4-04-444), and guar meal (S-05-687) and were formulated to provide either 18 Meal of metabolizable energy/head/day and 0.6 kg of digestible protein or 9 Meal of metabolizable energy/head/day and 0.37 kg of digestible protein (table II). All of the cows were brought daily into a dry lot and sorted within supplemental energy level into four preassigned groups (approximately 24 cows per group) according to cow body condition (poor or moderate) and ration (monensin or control). Thus the cows were sorted into the 8 groups outlined in table I before they were fed the concentrate portion of the supplement. The cows receiving 9 Meal/head/day of supplemental energy were fed the hay portion of
92
AUGUST 1980 VOL. 14 NO. 2
THERIOCENOLOGY
the ration while in these groups; whereas the cows receiving 18 Meal/head/day of supplemental energy were fed hay together after returning to pasture. The level of hay was decreased by one half at the start of the breeding season due to a hay shortage and additional grain added to the ration in order to maintain the appropriate supplemental energy level in each group. Cows in the monensin group received an average of 125 mg of monensin/head/day in the concentrate portion of the supplement. Rumen samples were obtained from 20 cows at the start of the breeding season and assayed for acetic, butyric, and propionic acid. Cow body condition was subjectively determined at the start of the experiment by one technician. The fat cover over the back and ribs was manually palpated and cows were assigned a body condition score ranging from 1 to 9 indicating the lowest to highest body condition, respectively. Cows having body condition scores of 4 or less were considered in poor body condition whereas cows having body condition scores of 5 or greater were considered in moderate body condition. Estrus detection was conducted twice daily using homosexual activity as an indicator, The cows were artificially inseminated by one of three technicians approximately 12 hr after estrous detection. Cows were randomized so that approximately an equal number in each group were bred by each technician to each bull. Pregnancy diagnosis per rectum was conducted 45-60 days postinsemination. Statistical analysis of the data involved Chi Square Analysis, and Analysis of Variance using Duncans Multiple Range Test to determine differences between means (15). Results
and Discussion
Cow body condition scores ranged from 3 to 7 at the start of the experiment and from 4 to 7 at the end of the experiment. cows receiving 18 Meal/head/day of supplemental energy gained an average of 25 kg and the weight change for cows within the monensin and control groups was similar (P>.O5, table III). Cows receiving 9 Meal/head/day of supplemental energy lost an average of 7 kg during the first half of the breeding season and gained an average of 17 kg during the second half of the breeding season for an overall average weight gain of 10 kilograms. The weight change was similar for cows within the monensin and control groups (P>.OS). The large amount of variation in weight change within groups should be noted (table III). The cows were maintained on pasture and undoubtedly the pasture and supplement intake varied between cows. The group receiving only 9 Meal/head/day of supplemental energy gained from 12 to 22 kg during the second half of the breeding season. The nutrient intake from the pasture probably increased during this period since the pasture was beginning to improve thus increasing energy intake. Regardless of energy level, the cows receiving monensin had higher (P<.O5) propionic acid levels and lower (Pc.05) acetic and butyric acid levels in the ruminal fluid than the control animals; consequently, total volatile fatty acids were similar (table IV).
AUGUST
1980 VOL.
14 NO. 2
93
THERIOGENOLOGY
Level of supplemental energy significantly influenced the pregnancy rate, pregnancy rate at first service, and the percent conceptions per estrus, whereas monensin and cow body condition did not. An increase of 19 percentage units in pregnancy rate (P<.OOS), 19 percentage units in pregnancy rate at first service (Pc.01) and 12 percentage units in conceptions per estrus (Pc.005) were noted in cows receiving 18 Meal/head/day of supplemental energy compared to cows fed 9 Meal/head/day of supplemental energy (table V). Theoretically, the energy available to cows should be increased when they receive monensin. By receiving 9 Meal/head/day of supplemental energy (a deficient amount) a consequential increase in energy should be available to cows receiving monensin. Consequently, the weight gains and reproductive performance limited by low energy intake might be improved. Conversely, no difference between monensin and control groups would be expected in the cows receiving 18 Meal/head/day of supplemental energy since the energy intake would probably be adequate. Weight gains and reproductive end points (pregnancy rate, pregnancy rate at first service, and conceptions/ estrus) were similar for the monensin and control groups that received In fact, all three reproductive 9 Meal/head/day of supplemental energy. end points in the cows receiving 9 Meal/head/day of supplement tended to be higher in the control cows than in the cows receiving monensin (P>.OS, table VI). An important finding of this study was the increase in reproductive performance for cows in poor body condition and receiving a supplement of 18 Meal/head/day. The pregnancy rate after 45 days of breeding was 19 to 33 percentage units higher in the cows in poor body condition receiving 18 Meal of supplemental energy/head/day than in the other three groups (Pc.05, table VII). Similar differences in pregnancy rate at first service (Pc.05) and conceptions per estrus (Pc.05) were noted. The increase in the conception rate of poor body condition cows receiving 18 Meal/head/day of supplemental energy is similar to the results reported in postpartum beef cows receiving 150% of the NRC requirements (21). However, the length of feeding time and/or feed level necessary to obtain an increase in conception rate is unknown Feeding monensin (125 mg per day) did not increase (P>.OS) weight gain, pregnancy rate, pregnancy rate at first service nor the percentage of conceptions per estrus in nonlactating beef cows fed either 9 or 18 Meal/head/day of supplemental energy. Other workers have noted an increase in weight gain with cows receiving roughage rations (16), growing cattle on pasture (8, 11) or growing heifers fed hay (17). In feed lot cattle, no increase in weight gain has been reported, however, feed efficiency has been improved (2, 12). The failure to find a weight change response in this study could be a result of the lower level of monensin fed (125 mg vs 200 mg in The increases in propionic other studies) or the ration composition. acid in the rumen of 32% and 48% are similar to the increases reported by other workers (4, 10, 12, 16, 17). Thus, the 125 mg of monensin fed in this study was as effective at increasing propionic Alternativeacid levels as the 200 mg of monensin fed in other studies. ly, factors other than an increase in propionic acid may be important in increasing weight gain in cows fed monensin. It has been reported
AUGUST 1980 VOL. 14 NO. 2
THERIOGENOLOGY
that the addition of monensin to a roughage ration decreased feed intake and animal performance (9). The rations fed in the present study were different than those in other studies; therefore, no direct comparison could be made. Other workers have reported increased reproductive performance in animals receiving monensin; however, the improvements were in the onset of the postpartum estrus (16) and a decrease in puberal age (7). The endocrine mechanisms regulating the onset of puberty and the onset of estrus may be different than the mechanisms regulating conception even though an improvement in weight gain has been reported to be important in each case (1, 5, 20, 21). The failure of cow body condition to effect the reproductive end points studied here was not unexpected (19). Most cows in poor body condition had achieved moderate body condition by the end of the study which may have been one reason there was no difference in reproductive performance between the two body condition groups. The lower reproductive performance in cows fed 9 Meal/head/day of supplemental energy compared to cows receiving 18 Meal/head/day of supplemental energy is similar to that noted by other workers. Numerous workers have reported that underfeeding prior to and during the breeding season decreases the pregnancy rate in cows and heifers (6, 14, 18). The effect of feeding different energy levels for varying lengths of time on pregnancy rate in beef cows needs to be explored more thoroughly and the hormonal mechanism elucidated.
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1980 VOL.
14 NO. 2
9s
THERIOGENOLOGY Literature
Cited
1. Arije, G. F. and J. N. Wiltbank. 1971. in Hereford heifers. J. Anim. Sci.
Age and weight at puberty 33:401.
2. Brown, H. L., L. H. Carroll, N. G. Elliston, H. F. Grueter, J. W. McAskill, R. D. Olson and R. P. Rathmacher. 1974. Field evaluation of monensin for improving feed efficiency in feedlot cattle. Proc. Western Section, ASAS 25:300. beef 3. Burrell, W. C. 1977. The effect of monensin in lactating cows in poor body condition receiving low levels of energy. Ph.D. Dissertation, Texas A&M University, College Station. 4. Dinius, D. A., M. E. Simpson and P. B. Marsh. 1976. Effect of monensin fed with forage on digestion and the ruminal ecosystem of steers. J. Anim. Sci. 42:229. 5. Dunn, T. G., J. E. Ingalls, D. R. Zimmerman and J. N. Wiltbank. 1969. Reproductive performance of 2 year old Hereford and Angus heifers as influenced by pre- and post-calving energy J. Anim. Sci. 29:719. intake. 6. Lamond, D. R. 1969. Sources of variation in reproductive performance in selected herds of beef cattle in north-eastern Australia. Australian Vet. J. 45:50. 7. Moseley, W. M., M. M. McCartor, R. D. Randel. 1977. Effects monensin on growth and reproductive performance of beef J. Anim. Sci. 45:961. heifers.
of
8. Oliver, W. M. 1975. Effect of monensin on gains of steers grazed on Coastal Bermudagrass. J. Anim. Sci. 41:999. 1977. Performance 9. Oltjen, R. R., D. A. Dinius and H. K. Goering. of steers fed crop residues supplemented with nonprotein nitrogen, minerals, protein and monensin. J. Anim. Sci. 45:1442 1976. Effect of 10. Perry, T. W., W. M. Beeson and M. T. Mohler. monensin on beef cattle performance. J. Anim. Sci. 42:761. 11. Potter, E. L., C. 0. Cooley, L. F. Richardson, A. P. Raun and R. P. Rathmacher. 1976. Effect of monensin on performance of cattle fed forage. J. Anim. Sci. 43:665. 12. Raun, A. P., C. 0. Cooley, E. L. Potter, R. P. Rathmacher and 1976. Effect of monensin on feed efficiency L. F. Richardson. of feedlot cattle. J. Anim. Sci. 43~670. 13. Richardson, L. F., A. P. Raun, E. L. Potter, C. 0. Cooley and R. P. Rathmacher. 1976. Effect of monensin on rumen fermentation in vivo. J. Anim. Sci. 43~657. --in vitro and --
96
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1968. Some factors 14. Schilling, P. E. and N. C. England. reproduction in beef cattle. J. Anim. Sci. 27:1363. 1960. Principals 15. Steel, R. G. D. and J. H. Torrie. McGraw-Hill Book Co., New York. of Statistics.
affecting
and Procedures p. 360.
16. Turner, H. A., R. J. Raleigh, and D. C. Young. 1977. Effect of monensin on feed efficiency for maintaining gestation mature cows wintered on meadow hay. J. Anim. Sci. 44:338. 17. Utley, P. R., G. L. Newton, R. J. Ritter, III and W. C. McCormick. 1976. Effects of feeding monensin in combination with zeranol and testosterone-estradiol implants for growing and J. Anim. Sci. 42~754. finishing heifers. 1967. 18. Warnick, A. C., R. C. Kirst, W. C. Burns and M. Koger. Factors influencing pregnancy in beef cows. J. Anim. Sci. 26:231 (Abstr.). 1975. 19. Whitman, R. W., E. E. Remmenga, and J. N. Wiltbank. Weight change, condition and beef cow reproduction. J. Anim. Sci. 41:387 (Abstr.). 20. Wiltbank, J. N., W. W. Rowden, J. E. Ingalls, K. E. Gregory, and R. M. Koch. 1962. Effect of energy level on reproductive phenomena of mature Hereford cows. J. Anim. Sci. 21:219. 21. Wiltbank, J. N., W. W. Rowden, J. E. Ingalls and D. R. Zimmerman. 1964. Influence of postpartum energy level on reproductive performance of Hereford cows restricted in energy intake prior to calving. J. Anim. Sci. 23:1049.
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THERIOGENOLOGY
TABLE I.
EXPERIMENTALDESIGN
Supplemental energy level (Meal ME/hd/day)
Cow body condition Moderate Poor 9 Meal 18 Meal 9 Meal 18 Meal
Treatment Monensin
aa
24
19
22
Control
24
24
22
23
a No. cows/treatment
group
AUGUST 1980 VOL. 14 NO. 2
THERIOGENOLOGY
FJ . M
u-i d
-r . %-I
r-7
d
w-2
2.
In
N
0
d
01
2.
0
hl M
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1980 VOL.
14 NO. 2
m
In
0 m
%.
99
THERIOGENOLOGY
TABLE III. COW WEIGHTCHANGES FOR THE 53 DAY PERIODNEARTHE BREEDINGSEASON
Weight change (kg) Before to middle of breeding season (26 days) Supplemental energy 18 Meal o:,-.&/head/day
Middle to end of breeding season (27 days)
Beginning weight (kg)
Monensin Moderate condition Poor condition
(kg)
(kg)
374 -+ 46
11 + 12a
14 + - 7
326 -+ 41
13 -+ 10
14 -+ 8
386 -+ 54
12 + 11
15 -+ 31
340 -+ 43
10 -+ 12
11 + 8
359 -+ 49
-4 -+ 15
12 -+ 14
327 -+ 38
-4 -+ 8
17 -+ 8
368 -+ 36
-14 -+ 8
17 -+ 9
324 -+ 39
.-7 -+ 11
22 -+ 11
Control Moderate condition Poor condition
(kg)
(kg)
Supplemen+ energy 9 Meal of ME/head/day Monensin Moderate condition Poor condition
(kg)
(kg)
Control Moderate condition Poor condition
(kg)
(kg)
a Standard deviations
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1980 VOL.
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THERIOGENOLOGY
m . m +I c-4 .
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1980 VOL.
14 NO. 2
d . m +I 00 .
101
Moderate condition Poor condition
c,d
Figures
in the same column having different
superscripts
superscripts
71 69
18 Meal/head/day 9 Meal/head/day
in the same column having different
50 47
80a 61b
Monensin Control
Figures
63c 44d
70 70
Treatment
a,b
50 57
Pregnancy rate (%)
are different
are different
(Pc.01).
(P<;bD5).
49 54
58a 4tjb
50 54
Conception per estrus (%I
EFFECTOF MONENSIN,ENERGYLEVEL, AND COWBODYCONDITION ON REPRODUCTIVE ENDPOINTS
Pregnancy rate at 1st service ("a)
TABLE V.
THERIOGENOLOGY
TABLE VI.
EFFECTOF MONENSINON PREGNANCY RATE, PREGNANCY RATEAT FIRST SERVICE, AND CONCEPTIONS PER ESTRUSIN COWSFED EITHER 9 MCAL OR 18 MCAL OF SUPPLEMENTAL ENERGYPER HEADPER DAY
Treatment
9 Meal/head/day
Energy level (%) lb'Mcal/head/day
pregnancy rate 45day
period
Monensin
5ga
a2b
Control
63
78
Pregnancy rate
(first
service)
Monensin
37a
62b
Control
50
64
Conceptions
per estrus
Wnensin
43
56
Control
48
60
a,b
Figures in the same row having different different (Pc.05).
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1980 VOL.
14 NO. 2
(%)
superscripts
are
103
Moderate
18 Meal/head/day
73b
96a
in same column having different
Poor
18 I&al/head/day
Figures
Moderate
g.Mcal/head/day
"b'c
Poor
Cow body condition
superscripts
Pregnancy rate 45 days 01
are different
54ab
7za
Pregnancy rate (1st service) e-1
(Pc.05).
50b
7oa
Conceptions per estrus 0)
EFFECTOF SUPPLEMENTAL ENERGYLEVEL AND COWBODYCONDITION ON REPRODUCTIVE ENDPOINTS
9 Meal/head/day
Supplemental energy level
TABLEVII.