E F F E C T O F T O T A L D I G E S T I B L E N U T R I E N T I N T A K E F R O M B I R T H TO F O U R Y E A R S O F A G E ON G R O W T H A N D R E P R O D U C T I V E

D E V E L O P M E N T A N D P E R F O R M A N C E O F D A I R Y B U L L S a

R. J. F L I P S E AND ft. O. ALI~IQUIST

Dairy Breeding Research Center, Depar tment of Dairy Science The Pennsylvania State University, University Pa rk

SUMMARY

Neonatal Holstein bull calves were assigned to four levels of energy intake repre- senting 70, 100, 115, and 130% of the National Research Council recommended TDN allowances for growing dairy calves. The groups were designated L, N, M, and H, respectively. Two additional groups were on a changeover at 104 wk. of a g e - - L i t changed from 70 to 130% and H L from 130 to 70%. Data were collected on growth (body weight, height at withers, and heart gir th) , onset of semen production, and semen quanti ty and quality until the bulls reached 208 wk. of age. The average age at the onset of semen production was 61, 45, 41, and 44 wk., respectively, for the L, N, M, and H groups. Comparable figures for body weight a t the onset of semen production were 523, 643, 675, and 784 lb.

At 80 wk. of age, the average motile sperm output per ejaculate was 1.15 billion for the L group; this was about 50% of that for the t I group. Af ter 112 wk. of age there was no difference in output of motile sperm per ejaculate associated with level of energy intake.

Between 156 and 208 wk. of age, the H bulls became much slower in sexual reaction time than bulls in other groups. During this period weaknesses of the feet and legs also became evident in the H bulls. Depletion trials at 4 yr. of age confirmed the rela- tively low sexual responses of the H bulls and also showed that M as well as H bulls were deficient in their abil i ty to recover response af ter satiation to a stimulus animal. Sperm output and extra-gonadal sperm reserves were similar among bull groups.

Limited fert i l i ty data collected on the L, N, and H groups showed no marked differ- ence in fer t i l i ty attributable to the level of TDN intake.

W i t h i n the p a s t decade much i n t e r e s t has cen te red on the effects of n u t r i t i o n on r e p r o d u c t i v e p e r f o r m a n c e of f a r m an imals . A n u m b e r of rev iews on va r i ous aspec ts of th i s sub jec t have a p p e a r e d ; those of Re id (19) , Reece (18) , a n d Cas ida (5) p r o v i d e c u r r e n t a p p r a i s a l s of th is a r e a of inves t iga t ion . A s d e l l et al.

(1) have d iscussed a coopera t ive r eg iona l a p p r o a c h to the p rob lem. Much of t he work w i th ca t t l e has invo lved m e a s u r i n g the response to va r i a -

t ions in the p l a n e of n u t r i t i o n , a l t h o u g h the resu l t s c o m m o n l y a r e a t t r i b u t e d to v a r i a t i o n s in e n e r g y in take . The r a t i o n a l e fo r the i m p l i c a t i o n of e n e r g y (19) has been based on the idea t h a t on ly a l i m i t e d n u m b e r of specific n u t r i e n t s a r e invo lved in r e p r a d u c t i o n ; some of t he n u t r i e n t s which a r e invo lved inf luence a p p e t i t e and, thus, the ene rgy in take .

Received for publication November 25,'1960.

1Authorized for publication on November 16, 1960, as paper No. 2507 in the journaI series of The Pennsylvania Agricultural Experiment Station.

Supported in part by funds from the regional project NE-1 entitled Causes and Pre- vention of Reproductive Failures in Dairy Cattle, a cooperative study involving Agricultural Experiment Stations in the Northeastern region and the Dairy Husbandry Research Branch, U. S. Department of Agriculture.

905

906 R. J. FLIPSE AND J. O. ALMQUIST

The present study was undertaken in 1950 to determine specifically the effects of variations in energy intake on the growth, reproductive development, and reproductive performance of Holstein bulls, whereas other nutrients were maintained at adequate and similar levels in all experimental groups. The last replications completed the 4-yr. experimental period in 1958.

EXPERIMENTAL PROCEDURE

Four levels of energy intake, expressed as total digestible nutrients, were tested as to their effects on growth, reproductive development, and subsequent reproductive performance of Holstein bulls. The control group (N) received the National Research Council recommended allowance for total digestible nutrients (TDN) (12). The low group (L) received 70% of this allowance, whereas medium (IV[) and high (H) groups received 115 and 130%, respectively. Protein and mineral intakes exceeded the recommended allowances for these nutrients and were similar in all groups. Composition of the rations and details of feeding and management have appeared in a preliminary report (8).

Space limitations prevented keeping all 24 experimental animals on trial for the full 4-yr. period of experimentation. Thus, as bulls reached 2 yr. (104 wk.) of age, random assignments (within each of the four main groups) were made as follows :

Change made Exper imenta l at 104 wk. Subgroup No. of

group of age designation bulls

L No change L 3 To H LI{ 3

:N No change N 3 Removed f rom expt. .. 3

M No change M 3 Removed f rom expt. 3

H No change H 3 To L H L 3

Where changes in feeding program were made (LH and HL subgroups), they were done gradually over the 8-wk. period of 105 to 112 wk. of age. Ration changes were made at 2 yr. of age, to ascertain what effects a specified level of energy would have on reproductive performance, and the extent to which early nutrition might influence subsequent performance on a different energy level.

Sexual development and semen production were evaluated as previously reported (8). In addition, starting at 3 yr. of age, sexual activity was measured using reaction time to ejaculation with a constant stimulus animal. However, in some cases it was necessary to introduce a new stimulus animal in order to achieve ejaculation. Sexual preparation consisted of 2 rain. of restraint and one false mount before ejaculation.

Upon reaching 4 yr. of age, two 2-hr. depletion trials at a seven-day interval were conducted with each bull to gather data on sperm output, sperm reserves, and behavioral characteristics (9). During the first depletion trial, the bull

EFFECT OF NUTRIENT INTAKE ON PERFORMANCE OF BULLS 907

was p e r m i t t e d to e j a c u l a t e v o l u n t a r i l y w i th a cons t an t - s t imu lus a n i m a l for

2 hr. or u n t i l s a t i a t e d (no response in 30 ra in . ) . One week l a te r , r ecove ry of sexua l response to the same s t i m u l u s a n i m a l was m e a s u r e d by c o m p a r i n g the

n u m b e r of e j acu la t e s ob t a ined d u r i n g the f i rs t hou r of the second t r i a l w i th the n u m b e r ob t a ined d u r i n g the f i rs t hou r of the f i rs t t r i a l . A f t e r 1 hr. w i t h the i n i t i a l an imal , r esponse to new s t imu lus a n i m a l s was d e t e r m i n e d i m m e d i a t e l y

b y offer ing t h r e e new an ima l s a t 20-min. in te rva l s . E x t r a - g o n a d a l s p e r m rese rves were ca l cu l a t ed on the basis of s p e r m ou tpu t , u s i n g the va lue r e p o r t e d b y H a l e a n d A l m q u i s t (9 ) , t h a t an ave rage of 53.4% of t he t o t a l s p e r m reserves is r emoved b y a d e q u a t e dep le t ion .

RESULTS

F e e d i n t a k e was c a r e f u l l y r e g u l a t e d t h r o u g h o u t t he e x p e r i m e n t ; each ani- m a l ' s r a t i o n was a d j u s t e d week ly on the bas is of his body weight . A c t u a l feed i n t a k e a t 104 wk. was w i t h i n 0 .5% of the p r e s c r i b e d levels of 70, 100, 115, a n d 130% of t he r e c o m m e n d e d a l lowance fo r TDN. F r o m 2 to 4 yr . of age, feed con- s u m p t i o n was m a i n t a i n e d in a l l b u t the H group , when c o n s u m p t i o n dec l ined s l igh t ly . D u r i n g the 4 yr . of t he t r i a l the H g r o u p consumed an a ve ra ge of 128% of the r e c o m m e n d e d a l lowance.

The s u m m a r i z e d d a t a on body weight , he igh t a t wi thers , a n d h e a r t g i r t h a r e p r e s e n t e d in Tab le 1. A s wou ld be expected , the g rea t e s t d i f ferences occu r r ed d u r i n g the p e r i o d of most r a p i d growth . F o r example , a t 48 wk. t he L g r o u p

TABLE 1 Body weight, height at withers, and heart girth of Holstein bulls, on various

levels of TDN intake (Mean of three bulls per group)

Age in Group weeks L N M H LH HL

Weight (lb.) 0 96 95 102 105 102 96

48 ~28 669 819 831 395 843 96 876 1,276 1,510 1,557 847 1,635

112 1,003 1,438 1,708 1,791 1,077 1,762 160 1,30.9 1,776 2,185 2,164 1,757 1,844 208 1,46~ 1,945 2,424 2,488 2,117 1,869

Height at withers (c~.) O 74 76 76 77 75 74

48 107 116 123 122 107 120 96 128 135 142 140 127 137

112 134 140 148 145 133 142 * 160 143 145 155 151 146 148 208 148 149 157 155 153 151

Heart girth (vm.) 0 81 81 84 84 81 81

48 132 157 168 165 135 168 96 170 198 206 208 173 211

112 178 203 213 216 185 216 160 197 216 23~ 235 220 219 208 203 226 244 246 236 221

908 1~. J. FLIPSE AND J. O. ALMQUIST

averaged 63% of the body weight of the N group. A t 96 wk. this f igure had

increased to 69%, and at 208 wk. to 75%. S imi la r to f indings wi th beef catt le (22), bul l s res t r ic ted in energy for the first 2 yr. ( L H ) recovered complete ly

when fed l ibe ra l ly a f t e r 2 yr. of age. Growth pe r fo rmance for both the M a n d

H groups was above the Morr ison average (16), whereas the N group was s l igh t ly below this average.

The age, body weight, height a t withers, a n d hear t g i r th a t the t ime the first

e jacu la te c o n t a i n i n g moti le spermatozoa was collected are shown in Table 2.

TABLE 2 Age and measurements of Holstein bulls on various levels of TDN intake at the time the

first ejaculate containing motile sperm was collected

First ejaculation

Feeding No. Ht. at Heart level bulls Age Weight withers girth

(wk.) (lb.) (cm.) (cm.) L 8 61_+4 ~ 523_+40 114-+3 144-+4 N 8 45-+3 643-+41 114-+1 153----+-3 M 6 41-+2 675-+42 117-+2 155-+4 H 8 44-+2 784-+-41 119-+1 163-+3

a Mean and standard error.

The difference in age between the L and each of the other groups was s igni f icant

a t the 1% level of probabi l i ty . The other s ta t i s t ica l ly s ignif icant differences

were : weight , L and H (p 4 0 . 0 1 ) ; weight, L and M (p ~ 0.05), a n d hear t

gir th , L and H (p ~ 0.01). As observed by B r a t t o n et al. (4) , the he ight a t wi thers d id no t v a r y g rea t ly wi th T D N intake.

D a t a on total moti le sperm o u t p u t per e jacu la te are shown i n Table 3. As prev ious ly no ted (8) , bul l s on res t r ic ted energy in t ake p roduced poorer qua l i t y

semen t h a n did more l ibe ra l ly fed bul ls ear ly in the tr ial , b u t as the bul ls became

older th is difference disappeared. The change f rom H to L at 2 yr . of age ap-

peared to have an adverse effect on voiume of semen; this is reflected in tota l moti le sperm o u t p u t ( H L group, Table 3).

TABLE 3 Average output of motile sperm in billions per ejaculate of Holstein bulls

on various levels of TDN intake (Mean of three bulls per group)

Age in weeks

Group 57-80 81-104 105-112 113-136 13.7-160 161-184 185-208 113-208

L 1.01 3.24 4.56 4.35 4.88 4.71 5.62 4.76, -+ 1.32 ,a N 1.10 2.45 2.67 2.96 3.62 3.72 3.85 3.651 -+ 0.85 M 2.21 2.85 3.92 4.65 4.83 5.07 6.12 5.11 -+ 1.85 H 2.30 3.94 3.85 4.66 4.62 4.09 5.17 4.56 -+ 1.32 LH 0.93 1.23 1.96 3.07 3.61 4.43 4.99 4.00 -+ 0.21 ITL 2.26 3.51 3.27 3.78 3.41 4.40 4.99 4.14 -+ 1.2'3

Standard error.

E F F E C T O~ N U T R I E N T I N T A K E ON P E R F O R M A N C E OF B U L L S 909

Sexual behavior informat ion measured by reaction t ime to ejaculation is shown in F igure 1. Collection of these data was init iated at 3 yr. of age, when it became obvious tha t the reaction time of the H bulls was increasing. Sig- nificant differences were noted in the time required for ejaculation, with a mean of 9.2 rain. for H, 3.7 min. for M, and 1.5 rain. or less for each of the other groups.

Dur ing the 4th yr. of the experiment, each of the bulls in the H group developed visual evidence of weakness of the feet and legs. Whether these weaknesses were coincidental to, or the par t ia l cause of, lowered sexual act ivi ty rat ings and increased time for ejaculation is subject to speculation.

The data obtained f rom the depletion trials, presented in Tables 4 and 5, confirm and extend those obtained by weekly semen collections and measures of sexual reaction time. In general, sperm output and reserves were similar for all groups. Al though only one bull in the H group was sufficiently active to provide adequate depletion data, his sperm reserve was comparable to those

9

,o.,..

0

BIo

L N M H LH HL

I

1

FIG. 1. Reaction time per ejaculate (mean and standard error) for Holstein bulls on various levels of TDN intake.

910 R. J. FLIPSE AND J. O. AL1V~QUIST

of b u l l s i n o t h e r g r o u p s . T w o o f t h e L H b u l l s w e r e s l i g h t l y d e f i c i e n t i n s e x u a l

a c t i v i t y i n t h e f i r s t d e p l e t i o n a n d s h o w e d l ow s p e r m o u t p u t , b u t t h e y r e s p o n d e d

s u f f i c i e n t l y i n t h e s e c o n d d e p l e t i o n to s h o w t h a t t h e y w e r e n o t l a c k i n g i n s p e r m

r e s e r v e s . A l l b u l l s w h i c h p o s s e s s e d s u f f i c i e n t s e x u a l a c t i v i t y t o g i v e a d e q u a t e

d e p l e t i o n m e a s u r e s i n b o t h t h e f i r s t a n d s e c o n d t r i a l s , i n c l u d i n g t w o M b u l l s

a n d o n e H b u l l , s h o w e d c o m p l e t e o r e s s e n t i a l l y c o m p l e t e r e p l e n i s h m e n t of s p e r m

r e s e r v e s i n s e v e n d a y s . T h e r e f o r e , t h e r e w a s n o e v i d e n c e t h a t a n y of t h e b u l l s

o n t h e e x p e r i m e n t w e r e d e f i c i e n t i n s p e r m p r o d u c t i o n o n t h e b a s i s of 1 wk. of

r e p l e n i s h m e n t of d e p l e t e d s p e r m r e s e r v e s .

TABLE 4

Sperm output and reserves at 4 yr. of age as measured by depletion trials a t a seven-day interval

Group

Est. extra- 1st depletion 2nd depletion gonadal

sperm Av. No. Av. No. reserves

Av. No. of sperm Av. No. of sperm in of ejac. in billions of ejac. in billions billions ~

L 11 40.9 16 40.8 76.4 N b 17 39.7 25 37.0 71.8 M 8 30.5 11 36.0 75.1 tI¢ 7 35.1 9 38.6 72.2 LH 8 26.7 14 35.8 66.9 HL 22 42.2 27 37.3 74.4

a Based on sperm output for adequate depletion in one or both trials. b One bull excluded because of inadequate depletion in first trial. ¢ Represents only one bull, as other two were too inactive to be depleted.

T h e M a n d H g r o u p s s h o w e d d i s t i n c t l y i n f e r i o r a b i l i t y to r e c o v e r s e x u a l

r e s p o n s e to t h e s a m e s t i m u l u s a n i m a l i n 1 wk. ( T a b l e 5 ) . T h e o n l y b u l l s f a i l i n g

to r e s p o n d w e l l to t h e i n t r o d u c t i o n o f n e w s t i m u l u s a n i m a l s w e r e o n e t I b u l l

a n d o n e L H bu l l . A l t h o u g h w i d e v a r i a t i o n i n r e c o v e r y w a s e x p e c t e d ( 9 ) , n o n e

of t h e b u l l s i n t h e M or H g r o u p s a p p r o a c h e d 1 0 0 % r e c o v e r y , w h e r e a s a t l e a s t

TABLE 5

R e ~ v e r y ~ f s e x u a ~ r e s p ~ n s e a f t e r s a t i a t i ~ n a n d r e s p ~ n s e t ~ n e w . s t i m u l u s a n i m a ] s a t 4 y r . ~ f a g e

Group

Av. 5!o. Av. No. Per cent of ejac. of ejac. recovery in 1 hr. 1st hr. 1st. hr. with three of 1st of 1st successive

depletion depletion new S.A. a

L 8 74 9 N 8 74 14 M 7 47 10 H b 5 38 4 LI t 7 80 7 t IL 15 88 13

a Three new-stimulus animals (S.A.) presented in succession for 20-rain. each af ter 1 hr. with init ial test animal in second depletion.

b Represents two bulls; one bull not tested, as he failed to respond to a wide variety of stimuli before reaching 4 yr. of age.

EFFECT OF NUTRIENT INTAKE ON PEI~FOR~ANCE OF BULLS 911

one bull in each of the other groups showed 100% recovery. Nine of the 12 bulls in the groups other than M and H were higher in recovery than the highest bull in the M and H groups (57 % ). However, another H bull failed to respond to new-stimulus animals before reaching 4 yr. of age and could not be included in the depletion trials.

Data collected on the fer t i l i ty phase of the experiment were meager, with only two bulls each on the L, N, and H groups, and only 8,124 first services to the six bulls in the 2 yr. immediately following their re turn to the breeding organization. Fer t i l i ty data were as follows:

% 60- to 9O-day n o n r e t u r n s

Group means ,

No. 1st I nd iv idua l we igh ted Group Bul l services bulls by bulls

1 1,007 72.9 L 71.3

2 1,560 69.7

3 1,759 63.7 N 68.9

4 867 74.0

5 1,695 75.9 t t 72.6

6 1,242 69.2

Although individual differences are evident, it appears that the levels of energy intake employed had no drastic effect on subsequent ferti l i ty.

DISCUSSION

While the results in this s tudy have been at t r ibuted to differences in energy intake, a word of caution is in order, in that the nutr i t ive ratio varied inversely with the energy intake. This was necessary in order to va ry energy intake while maintaining equivalent intakes of protein and minerals. Whereas it is unlikely that nutr i t ive ratios vary ing within the range empk~yed (1:3 .6 for L to 1:6.0 for H) would affect reproductive performance markedly, the possi- bility has not been excluded by controlled experimentation.

Ignoring minor discrepancies, which may or may not be due to differences in experimental design, several studies are in general agreement with regard to the relationship between plane of nutr i t ion and onset of semen production (1, 4, 6, 10, 11, 13, 20). In general, low levels of feeding were observed to delay the onset of semen production 3 to 5 too. in comparison to moderate and high levels of feeding. The fact that similar differences were observed between the N and L groups in the present s tudy indicates that energy is the major limiting factor when intake is restricted. On the other hand, some investigations (4, 11) have indicated greater differences between normal and high planes of nutr i t ion than were shown between normal a~ld high levels of energy intake in the present

912 ~ . J . F L I P S E A N D J . O. A L M Q U I S T

study. I f such differences are actual ra ther than apparent , i t is logical to a t t r ibute them to the increased protein, minerals, and /o r vitamins supplied in the plane of nutr i t ion studies. Unpublished data (7) indicate tha t quant i ty of protein has little or no effect on the onset of semen production in bulls, but the specific effects of supplements of most minerals and vitamins, as well as nut r ient interactions, have not been determined.

With regard to sperm output, the adverse effects of low energy intake are obvious dur ing the early weeks of semen production. In this study, at 80 wk. of age the average motile sperm output per ejaculate for the L group was about 50% of that for the H group. James (10) reported similar results, and the data of Bra t ton et al. (4) indicated that underfed bulls produced about 50% as many motile sperm per ejaculate as did overfed bulls at 74-80 wk. of age. However, if one examines total motile sperm output f rom 113 to 208 wk. (Table 3), little difference can be noted between high and low levels of energy intake. This supports the observation of Mann and Walton (14) : severe underfeeding did not al ter the sperm output of a mature bull. One the other hand, Olson (17) stated that with mature monozygous triplets, semen quality and quant i ty favored bulls receiving 100 and 130% TDN over those receiving 70% TDN.

In this study, a maximum of one ejaculate per bull per week was collected, using a low level of sexual preparation. Thus, the relatively low sperm output values do not reflect possible effects of varying energy intake on the rate of sperm production. However, sperm output and extra-gonadal reserves as meas- ured by depletion trials at 4 yr. of age (Table 4) were not markedly affected by restricted energy intake. F u t u r e studies of this type should incorporate more demanding collection frequencies, with intensive preparation, in order to detect possible changes in semen characteristics and spermatogenesis (9). Using a part ial exhaustion technique to provide a more demanding collection fre- quency, VanDemark et al. (21) recently reported that the number of sperm collected from two underfed 3-yr.-old bulls was 77% of that collected from the normally fed controls. Fur thermore , reversal of the rations at 4 yr. of age did not correct deficiencies in the number of sperm collected f rom the previously underfed bulls.

I t would have been interesting to continue observation of these bulls over a longer period of time, par t icular ly in light of the effects of level of feeding on the ferti l i ty, onset of disease, and longevity of rats (2, 3, 15). F rom a practical standpoint, however, the development of weaknesses of the feet and legs and the lower level of sexual activity in the H group suggest that these factors would soon limit the useful l ife of these bulls.

Level of energy intake during early life apparent ly had little effect on the quali ty or quant i ty of semen produced later. Those bulls changed from L to H at 2 yr. of age did not show the slow sexual reaction time of those continually on H ; sluggishness may have developed in L H bulls, had the high energy feeding been continued over a longer period of time. In fact, some indication of this was observed in the depletion trials. A program of heavy feeding dur ing early life followed by restricted feeding later may have some merit. By moderate to

EFFECT OF NUTRIENT INTAKE ON PERFORMANCE OF BULLS 913

heavy early feeding, semen production is initiated at an early age, while re- stricted later feeding should prolong the useful life of the bull.

I t is apparent that high energy intake is not desirable for bulls past the stage of rapid growth, while subnormal energy intake in early life is disad- vantageous, in that it delays the onset of semen production. Ear ly liberal feeding, alone or in combination with hormonal stimulation (6), may be eco- nomically feasible (4) when it is imperative that semen be obtained at the earliest possible age.

ACKNOWLEDGMENT

The authors wish to acknowledge the cooperation of personnel a t the Western Pennsyl- vania Artificial Breeding Cooperative, Clarion, and the Southeastern Pennsylvania Artificial Breeding Cooperative, Lancaster, in conducting the fert i l i ty phase of this investigation.

REFERENCES

(1) ASI~LL, S. A., BUTTON, R. W., FRANK, A. H., MIXNF~, J. P., PFAU, K. O,, PLASTRIDGE, W. N., AN]) YA~S, V. J. Breeding Difficulties in Dairy Cattle--Their Causes and Prevention. Cornell Univ. Agr. Expt. Sta., Bull. 924. 1957.

(2) BF~G, B. N. Nutr i t ion and Longevity in the Rat. I. Food Intake in Relation to Size, Heal th and Ferti l i ty. J. Nutr i t ion, 71: 242. 1960.

(3) BFm~, B. N., AND S ~ S , It. S. Nutr i t ion and Longevity in the Rat. I L Longevity and Onset of Disease with Different Levels of Food Intake. J. Nutri t ion, 71: 255. 1960.

(4) BRA~I'OlV, R. W., MusG~v~, S. D., DUNN, H. O., ~ D FOOT~, R. tI. Causes and Pre- vention of Reproductive Failures in Dairy Cattle. I I . Influence of Underfeeding and Overfeeding from Bir th to 80 Weeks of Age on Growth, Sexual Development, and Semen Production of Holstein Bulls. Corned Univ. Agr. Expt. Sta., Bull. 940. 1959.

(5) CASmA, L. E. Effect of Feed Level on Some Reproductive Phenomena in Cattle) Sheep, and Swine. Reproductive Physiology and Prote in Nutri t ion, p. 35. Rutgers University Press. 1959.

(G) DAVIEPS, D. V., MANN, T., AND ROWSON', L. E. A. Effect of Nutr i t ion on the Onset of iYiale Sex Hormone Activity and Sperm Formation in Monozygous Bull-Calves. Proc. Roy. Soe., 147: 332. 1957.

(7) FLIPS~, R. 5., AND ALMQtrlST, ft. O. Unpublished data. Pennsylvania Agr. Expt . Sta. 1959.

(8) FLIPs]~, R. J., SI~YDE~, J . W., THACKE~ D. L., AND AL~QUIST, ft. O. Effect of Total Digestible Nut r ien t In take on Growth and Reproductive Development of Dairy Bulls. Pennsylvania Agr. Expt. Sta., Prog. Rept. 104. 1953.

(9) ITAL]~, E. B., AND ALMQUIST, 5. O. Relation of Sexual Behavior to Germ Cell Output in Fa rm Animals. The Effect of Germ Cell Damage on Animal Reproduction. J . Dairy Sci., 43: Supplement, p. 145. 1960.

(10) J A ~ S , J . P. The Effect of Level of Nutr i t ion on the Sexual Capacity of Dairy Bulls. Proc. New Zealand Soc. Animal Production, 10: 84. 1950.

(11) KOl~rS, E., AN1) ]tlLnFmRAN~, IT. H. Untersuchungen uber untersehiedliche Aufzueh- t in tens i ta ten an Zwillingsbullen unter besonderer Beruck-sichtigung ihres spateren Befruchtungsvermogens (Spermaqual i ta t ) . Kiel. Milchev. Forsch-Ber., 10: 481. 1958. [Abstract from Animal Breed. Abstrs., 28: 670.]

(12) LOOSLI, J. K., HU~F~A~, C. F., PETERSFAV, W. E., AND PHILLIPS, P. H. Recommended Nutr ient Allowances for Domestic Animals. I I I . Recommended Nutr ient Allowances for Dairy Cattle. Natl. Research Council Rept. 1950.

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914 R. J. FLIPSE AND J. O. ALMQUIST

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