Florida Agricultural Experiment
Station, Gainesville, Florida
The relationship of excessive and inadequate
levels of nutrition to potential reproductive potency in
beef bulls. -
James F. Hentges, Jr. /
J/ Text of paper presented before Southeastern Regional meeting
of Society for Study of Breeding Soundness of Bulls at
Gainesville, Florida on October 4, 1963.
2/ Hentges, Associate Animal Nutritionist.
This review is an endeavor to describe the progress of researchers
in solving practical bull fertility problems which demand immediate at-
tention and potential bull fertility problems which may be created by
new management practices.
In brief outline form, these problems are:
I, Emaciated or "wasted" physical condition of bulls.
A. Bulls so weak that ability to mount a cow is reduced
(of relative minor importance except under coastal range and
1. Frequently complicated with disease, infected in-
jury, lameness, internal and external parasites, etc.
2. Starvation ("hollow belly") conditions may exist
on ranges of sparse, lignified, frosted grasses when sup-
plemental feed is not provided,
a. Decline in libido, sperm concentration and % of
abnormal spermatozoa has been reported in dairy bulls
grazing low quality, low protein pastures.
b. U, of Fla. research with two groups of Angus
bull calves fed a control diet (13.7% crude protein)
and a protein deficient (1.6%) diet revealed an im-
mediate decrease of appetite 7,5 vs. 4,2 lb. feed/
day after 28 days. At the end of 26 weeks, average
intake was 9.78 lb. vs. 3,28 lb. or 1.86% vs. 1.13%
of body weight. Table 1 shows that physical weak-
ness of starved bulls on a protein deficient diet
caused a longer time interval to first mount and
time interval to first coitus indicating a decline
TABLE 1, LIBIDO DATA OF ANGUS BULLS FED CONTROL AND
PROTEIN DEFICIENT DIETS
Interval to Interval to Libido
first mount first coitus Score
Days on (minutes) (minutes) (1-5)
experiment Control Deficient Control D efiiCent- Control Deficient
28 2.0 0.7 5.1 4.4 4.4 4.7
182 0.7 2.8 3,8 10.0 4.9 3.2
Table 2 shows a decline of semen quality associated with weight
loss in Angus bulls on a starvation diet.
TABLE 2, EXCERPT FROM T. N. MEACHAM, Ph.D DISSERTATION, 1962
.ay of experiment
DIET 28 56 4 182
Low Volumel 6,6 6,8 4.9 -- 3,1
Protein Motility2 52 34 16 -- 20
(1,6%) Concentration3 729 1877 1187 -- 288
Live wt,, Av, 347 317 292 245
Control Volume 5 6 8 6 7 8 8.3
(13,7%) Motility 41 37 30 70
Concentration 455 1079 2039 1767
Live wt,, Av, 449 478 504 620
2 % motile cells. Low motility initially observed in all samples was
partially due to faulty technique in cold weather.
3 Sperm cells per ejaculate times 106,
Note that spermatogenesis was not halted even though four bulls died of
emaciation before study terminated. Once sexual maturity is attained,
spermatogenesis apparently is difficult to halt by a restricted energy
or total feed intake (Lack of vitamins and minerals in diet might mag-
nify effect on spermatogenesis).
Table 3 illustrates the point that spermatogenic capacity is de-
creased during malnutrition, This confirms recommendations to confine
breeding herds to smaller pastures of good quality forage (preferably
clover-grass) during breeding season so that bulls and females are
gaining in weights,
TABLE 3. RESULTS OF SEMEN EXHAUSTION STUDY ON ANTGUS BULLS BEING FED
ADEQUATE (CONTROL) AND PROTEIN DEFICIENT DIETS
Diet 1st day 2nd day Total
Control 4,5331/ 1,564 6,117
Protein deficient 1,190 568 1,759
1/ Total sperm cells per ejaculate x 106
- 4 -
3. Inherited faulty conformation which may impose a phy-
siological stress on range bulls -- extremely short-
legged, compact type,
4, True deficiencies of copper, cobalt, phosphorus
and vitamin A,
a. Failure to mount, low sperm concentration and high
count of abnormal spermatozoa observed when bulls fed
vitamin A deficient diets,
5. Excessive voluntary intake of toxic materials --
fluorine, arsenic, nitrate, molybdenum, copper, lead, lu-
6, Miscellaneous: too timid to eat supplemental feed
(species segregation, social order), loss of teeth, etc.
B. Thin bulls which mount but do not produce viable semen:
1. May occur for a period of time after an emaciated bull
is offered an adequate diet. Although germinal epithelium
in seminiferous tubules can recover snerm producing power,
a period of time may laose before mature spermatozoa ap-
pear in the semen in normal concentrations.
a. Sexual disorders occurred for as long as 5 months
after addition of vitamin A to diet of deficient pre-
pubertal bulls. The period was shorter for sexually
b. Yearling Angus bulls fed a protein deficient diet
exhibited rapid return of libido and motility within
2 months after an adequate diet was offered but sperm
concentration remained low after 3 months.
2. May be partially due to season of year.
a. Several researchers have reported that semen quality
of mature bulls decreased as day length shortened being
lowest in Winter and highest in Spring. Extremes of
temperatures and humidity in Summer lowered quality.
b, Spermatopenesis of Guernsey bulls was impaired by
continuous exposure to ambient temperature of 1000 F.
for two weeks or 860F. for five weeks. Sex drive was
not impaired but ejaculates of some bulls remained
practically void of sperm for two months after return
to normal environment.
- 5 -
c, Dairy bulls in Louisiana subjected to simulated sub-
tropical conditions of high temperature and high humidity
showed little reaction except in late summer and fall
months (July through November) when decrease in apparent
II. Excessively fat bulls a problem which has long Dlagued bulls
fattened for show, Problem may be intensified by some bull perfor-
mance testing races to attain high average daily gains for publicity
A. Physical impairment by overfeeding concentrates.
1, Long toes, weakened hind leg structure, corns.
2. When concentrates are self-fed, muscular weakness
from inactivity leaves bulls prone to injuries and
their eventual adaptation to ranch pasture conditions
a. Two year old Angus and Hereford bulls which were
full-fed concentrates grazed and exercised very little
compared with bulls which were full fed forage (pas-
ture and/or silage) and 8 lb. concentrates. The fat
concentrate-fed bulls had real eve-appeal and were
declared sound on basis of anatomical and semen (ob-
tained by electric ejaculator) examination yet only
1 in 10 had the ability to complete coitus in libido
checks during humid, hot weather. None of the bulls
fed limited concentrates required foot trimming and
every one mounted and mated an estrogenized heifer
3. Prolonged stress is endured in "letting down" or
catabolizing excess fat under most ranch conditions.
A grass diet during Fall and Winter in Florida probably
does not provide adequate digestible protein, vitamins and
minerals to "burn" the excess body fat in the required time.
Supplemental nutrients should be provided to ensure active
rumen microbial fermentation, synthesis of B complex vit-
amins, maintenance of citric acid cycle and normal levels
of circulating plasma protein.
4. Change of reticulorumen microflora from "concentrate
utilizers" to "roughage utilizers" requires time which
may be critical when fat bulls are abruptly subjected to
B. Impaired fertility from overfeeding of concentrates --
an area in need of research,
1, Believed to develop when full-feeding of concen-
trates is continued beyond 14-16 months of aoe which
corresponds to end of standard 140 day bull perfor-
2. Irregular conception may be result of impaired
physical condition preventing completion of coitus
rather than non-viable semen.
3. Elevated scrotal temperature due to excessive
fatness is one possibility in a hot, humid climate.
C, Effect of overfeeding on age of puberty, a factor which
is becoming important in progeny testing.
1. Initiation of spermatoqenesis, appearance of motile
spermatozoa in semen sex behavior pattern occurs at
earlier age in dairy bull calves fed diets providing
130-160% of Morrison's or NRC minimum nutrient requirements.
2. Restriction of nutrient intake delays puberty but
spermatooenesis and attainment of puberty is not mater-
ially affected if bull receives enough nutrients for
3, Mounting without erection or with coiled vlans penis
probably correlated with incomplete separation of sheath
and penis epithelium or persistent frenulum, The effect
of nutrition on these conditions in beef bulls is not
Faulty nutrition is evident in tests for reproductive potency.
A test for breeding soundness (potential potency) should include the
1. Anatomical examination including body conformation as well as
2, Evaluation of ejaculate (electric ejaculator assumed),
3. Assessment of physical strength thrift, vigor, libido.
4. Ability to complete coitus with heifer (estrogenized or in
estrus) within 5 mounts or maximum time of 10 minutes.
5, When possible, search of extended pedigree for ancestors with
inherited defects, study of dams production record to spot
irregular reproduction and evaluation of bulls own performance
6. Condemnation of a bull should be deferred until the fol-
lowing factors are considered: previous nutrition, previous
environment, ejaculation by artificial vagina if ejaculate
by electrical stimulation was unsatisfactory, breed and aqe.