Effects of Dietary Crude Protein, Breed, Parity, and Health Status on the Fertility of Dairy Cows1

Effects of Dietary Crude Protein, Breed, Parity, and Health Status on the Fertility of Dairy Cows’ B. A. BARTON,* H. A. ROSAR10,3 G. W. ANDERSON,4 B. P. GRINDLE, and D. J. CARROLL5 Animal, Veterinary, and Aquatic Sciences, University of Maine, Orono 04469

ABSTRACT

A study was conducted to determine the impact of dietary CP (13% vs. 20%), parity (first vs. second lactation or later), and breed (Holstein vs. Jersey) on the reproductive efficiency of dairy cows. Sixty-four cows were blocked by parity and breed and assigned to one of two treatments. Cows were removed from treatments on d 100 or 120 depending on pregnancy status. Cows were categorized by health status based on the occurrence of postparturient disorders. Plasma urea N concentrations were influenced by diet ( 8 . 6 vs. 21 mg/dl, 13 and 20% CP, respectively), parity, and breed. Reproductive indices were not influenced by diet except that days to first estimated ovulation increased for cows fed the 20% CP diet when health status was added to the model. Days to first observed estrus, first AI service, and cumulative pregnancy rate were affected by health status. Regression analysis for survival showed an interaction of diet and health status for days open. High CP diets tended to increase days open when cows had major health problems; otherwise, a high CP diet decreased days open. The implementation of a strict reproductive management program allowed high reproductive efficiency goals to be achieved regardless of plasma urea N concentrations. ( Key words: crude protein, reproduction, breed, health) Abbreviation key: BCS = body condition score, CRFS = conception rate at first AI service, DFE = days to first estrus, DFO = days to first estimated

Received August 21, 1995. Accepted April 26, 1996. ‘Maine Agricultural and Forestry Experiment Station Paper Number 1898. 2Current address: Purina Mills. Inc., PO Box 66812, St. Louis, MO 63166. 3Current address: Junta Agroempresarial Dominicana, Inc., 4805 NW 79 Ave., No. 14, Pobi #10072-X, Miami, FL 33166. 4Corresponding author. 5Department of Animal Sciences, Oregon State University. Corvallis 97331. 1996 J Dairy Sci 79:22252236

ovulation, DFS = days to first AI service, DO = days open, PR = cumulative pregnancy rate, PUN = plasma urea N, SC = AI services per conception. INTRODUCTION

Research has shown that high amounts of CP in the diets of early lactation dairy cows have resulted in a negative impact on fertility in some, but not all, cases (2, 9, 10, 15, 28). Factors other than protein status, such as age, breed, occurrence of health disorders, and quality of reproductive management, also influence cow fertility (23, 27). The goal of this study was to identify which factors, when interacting with protein concentration in the diet, could negatively influence reproductive performance. The major causes of unsatisfactory breeding performance are inadequate reproductive management and occurrence of health disorders, such as metritis and ovarian cysts (23). Herd programs for health management can significantly increase breeding efficiency ( 1 4 ) . Therefore, when investigating the influence of diet on reproductive performance, the major causes of decreased fertility need to be identified and controlled. Carroll et al. ( 6 ) reported that first lactation cows that were fed a 20% CP diet and that experienced a reproductive health disorder had a higher number of days to first estimated ovulation (DFO) than did cows fed the 13% CP diet ( 3 0 vs. 18 d, respectively). This increased number of days might have been due to an interaction of dietary CP and age or to reproductive health disorders. Our study was designed to test those observations. Therefore, the objectives of this study were 1)to evaluate the effects of CP concentration, breed, and lactation number on production and composition of milk and on physiological measurements, such as plasma urea N ( PUN), BW changes, and changes in body condition score ( BCS); 2 ) to evaluate the main effects and interactions of CP concentrations, breed, lactation number, and postpartum health status on fertility; and 3) to use regression analysis for survival to identify variables and interactions that most affect days open ( DO).

2225

2226

BARTON ET AL.

MATERIALS AND METHODS

Schering-Plough Animal Health, Union, N J ) and a n i.m. injection of 5 cc of vitamins A, D and E combined (500,000 IU/ml of vitamin A, 75,000 IU/ml of vitamin D, and 5 IU/ml of vitamin E; InjacomD; HoffmanLaRoche, Nutley, N J ) . First lactation heifers received both injections, but only a t parturition. Dry period (beginning 8 wk prior to expected parturition) rations were formulated to meet NRC ( 2 2 ) recommendations for dry cows. Rations fed during lactation were composed of a mixed grass-legume silage (predominately orchardgrass and red clover), corn silage, ground corn and oats, soybean meal, vitamin and mineral supplements, and salt. The 13% CP (low) and 20% CP ( h i g h ) rations differed only in the proportion of ground corn and soybean meal (Tables 2 and 3 ) . The forage to concentrate ratio was 50:50 ( D M basis); the forage fraction consisted of 53% corn silage and 47% grass-legume silage. Corn silage was 26.6% DM, 9.0% CP, and 27.9% ADF (DM basis); grass- legume silage was 30.4% DM, 14.7% CP, and 37.5% ADF (DM basis). Rations were isocaloric and formulated to meet NRC ( 2 2 ) requirements for all components except ADF. A trace mineral salt block was available to all lactating cows for ad libitum consumption. Total mixed rations were fed for ad libitum intake twice daily a t 0800 and 1600 h to ensure 10% orts. Feed intake and orts were recorded daily for the low and high CP groups. Forages and TMR were sampled every 2 wk for DM, CP ( 11, NDF, and ADF ( 2 5 ) and were adjusted for moisture content. Samples of concentrate were collected weekly and com-

Cows and Experimental Design Sixty-four dairy cows that calved within a 6-mo period (November to April) were blocked by lactation (34 primiparous and 30 multiparous) and breed (47 Holsteins and 17 Jerseys) and were assigned to one of two dietary treatment groups in a 2 x 2 x 2 factorial arrangement. Factor 1 was the CP concentration in the TMR (13% vs. 20961, factor 2 was lactation number (first lactation vs. second lactation or later), and factor 3 was breed (Holstein vs. Jersey). Cows were categorized by health status (healthy, minor problems, or major problems) based on the occurrence and treatment of reproductive disorders. All cows were fed the test rations from d 1 through 100 postpartum. Cows that were not pregnant by d 100 were fed the test ration until confirmed pregnant or until 120 d postpartum. Table 1provides a characterization of the cows by diet, lactation, and breed. After parturition, cows were housed in a free-stall facility (15 stalls per pen) with a fence-line feed bunk. A total of four pens (two per diet) were used during the course of the experiment. TMR and Feed Analyses

At drying off and at parturition, cows in second lactation or later were injected i.m. with 5 cc of BOSE@ (1 mg/ml of Se and 68 IU/ml of vitamin E;

TABLE 1. Characteristics of cows by diet, lactation, and breed experimental groups. 1 3 4 CP

2 0 4 CP

Lactation 1

Lactation 22

Lactation 1

Lactation 22

Holstein Jersey

Holstein Jersey

Holstein Jersey

Holstein Jersey

~

Cow, no. At calving Age, yra Lactation, no.a wk 1 BW, kgaJ' Body condition scorela Previous lactation production, 305 ME2 Milk, kgb Protein, kg Fat, kgb

13 2.2 1.0 524 2.73

4 2.1 1.0 369 2.75

5

10 4.1 2.9

3.7 2.8

2.1 1.0

615 2.40

398 2.40

539 3.17

8671 325 274

6444 309 240

asignificant lactation main effect ( P < 0.05). bSignificant breed main effect ( P < 0.05). 'Five-point scale ( 1 = thin to 5 = f a t ) . 2305-d Mature equivalent production for cows in lactation 22.

Journal of Dairy Science Vol. 79, No. 12, 1996

13

~

3 2.1 1.0 373 2.67

~

10 4.1 3.0

3.7 2.4

597 2.28

412 2.40

9023 319 288

SEM

__

5

5865 295 230

0.1 0.1 6

0.07

273 10 9

2227

CRUDE PROTEIN AND REPRODUCTIVE PERFORMANCE

TABLE 2. Composition of low and high CP TMR. Component

13% CP

20% CP

(kg of DM100 kg of ration) Grass-legume silage Corn silage Corn, ground Oats, ground Soybean meal (49% C P ) Dicalcium phosphate Limestone Mineral mix1 Magnesium oxide (56% Mg) Trace mineral salt2

23.20 26.50 37.34 5.40 5.40 0.36 1.01 0.45 0.03 0.31

23.20 26.50 21.08 5.40 21.69

... 1.01 0.78 0.03 0.31

IMineral mix composition: 15.5% P, 14.055 Ca, 3.0% Mg, 0.75% S, 0.6% K, 0.015% I, 0.004% CO, 0.025% Cu, 0.035% Fe, 0.2% Mn, 0.75% Zn, 0.006% Se, 660,800 IUkg of vitamin A, 165,000 IUAg of vitamin D, and 2500 IUkg of vitamin E (Legurnins; Agway Inc., Syracuse, NY 1. 2Trace mineral salt composition: 92% NaC1, 0.35% Zn, 0.34%Fe, 0.2% Mn, 0.033% Cu, 0.007% I, and 0.005% CO (Champions Choice@;A k z o Inc., Camp Hill, PA).

posited monthly for DM, CP, ADF, and NDF analyses using the procedures mentioned ( 1, 2 5). Minerals were determined using wet chemistry at the New York DHI Forage Laboratory (Ithaca, NY). Soluble N content of feeds was determined using a borate buffer (20), and silage DM was determined using toluene analysis ( 7 1. Sample and Data Collection

Cows were milked twice daily, and production was recorded daily from d 5 to 100 of the trial. Weekly composites on consecutive p.m. and a.m. milkings were collected and analyzed by infrared spectrophotometry for protein, lactose, and fat (DHI, Ithaca, NY). Blood was collected between 1000 to 1200 h into heparinized evacuated tubes via the coccygeal vein for determination of plasma progesterone and PUN. Samples were collected once every week beginning 2 wk prior to calving and then three times per week postpartum until cows were confirmed pregnant or had completed 120 DIM. Samples were kept on ice ( 1 to 2 h ) until centrifugation (5000 rpm for 10 min). Plasma was immediately frozen at -20°C. The PUN concentrations were measured by the hydrolysis of urea to ammonia by the urease-Berthelot method (kit number 640; Sigma Chemical Co., St. Louis, MO). Plasma progesterone concentrations were determined by solid phase 1251-labeled radioimmunoassay (Coata-Count progesterone kit; Diagnostic Products, Los Angeles, CA). The interassay coefficients of variation for plasma progesterone of midcycle cows (mean, 6.7 k 0.9 ng/ml) and pregnant control cows (mean, 12.3 k

1.3 ng/ml) were 13.0 and 10.7%; the intraassay coefficients of variation were 3.7 and 6.4%, respectively. Cows were weighed on 2 consecutive d; means for 2-d BW are reported. Cows were weighed and scored for body condition [five-point scale where 1= thin to 5 = fat (2911 every other week, starting at 2 wk precalving until the cows finished the trial. The BCS were means from the scores of three independent analyses. Reproductive Measures

From 10 d postpartum until confirmation of pregnancy at 0700 to 0900 h and at 1700 to 1900 h for approximately 1 h twice daily, all cows were observed for signs of estrus in areas that changed with the season. Whenever possible, cows were moved outside to a dirt paddock; in inclement weather, cows were removed from the feeding area to an indoor area on a cement floor covered with sawdust. In addition, farm staff monitored estrous behavior during the day and while cows were in holding pens prior to milking. Primary (standing) and secondary (mounting) signs were used to define estrus. However, cows were also observed for tertiary signs of estrus, such as mucus discharge, red swollen vulva, increased activity, and other behavioral changes. Cows detected in estrus in the evening were inseminated the next morning, and cows detected in estrus in the morning were bred in the evening. Cows still in estrus 24 h from the first observed estrus were inseminated a second time; both AI were counted as one service. This event occurred two times during the trial with the same cow. The reproductive health of all postpartum cows that had not been inseminated was monitored biweekly by palpation of the reproductive tract per rectum. Occurrence of parturient events and disorders, including dystocia and retained placenta, and postpartum disorders, such as ovarian cysts and uterine infections, were recorded. Treatment protocols for TABLE 3. Nutrient composition of low and high CP TMR. Chemical composition

13% CP

DM. %

50.0

20% CP 50.0

(5% of DM) CP Soluble protein, % of CP Estimated NE,, AlcaVkg

13.0 31.0 1.68 18.1 37.8 0.78 0.45 0.25 1.35

ADF NDF Ca P Mg

K

~

~

20.0 23.3 1.66 18.1 33.3 0.75 0.46 0.25 1.67

~~~~~~~

Journal of Dairy Science Vol 79, No. 12, 1996

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BARTON ET AL.

all disorders were established and uniformly applied throughout the experiment. Daily measurements of body temperature (1200 to 1400 h ) were taken from calving until each cow was confirmed pregnant; twice daily measurements of temperature were taken when a cow had a body temperature >39"C. Body temperatures were used in differential diagnoses and treatment regimens. Calving difficulty, or dystocia, was scored as (1 = no problem, 2 = slight problem, 3 = needed assistance, 4 = considerable force, and 5 = extreme difficulty). Cows were classified as experiencing dystocia if they had a score 23. Retained placenta, defined as fetal membranes that were not expelled within 3 h after parturition, was treated with an i.m. injection of 25 mg of PGFz, (Lutalyse@;The Upjohn Co., Kalamazoo, MI). If the placenta was still retained 6 to 8 h later, boluses containing tetracycline were placed in the uterus every other day until the placenta was expelled. Body temperature was recorded twice daily on those cows; if the temperature was >39"C, the cow was injected i.v. with a 50% dextrose solution containing a broad-spectrum antibiotic until temperature returned to normal. One additional treatment was given after the temperature had returned to normal. Body temperature was monitored twice daily for an additional 3 d after the last treatment. Metritis, or uterine infection, was categorized as severe, subacute, or subclinical based on the nature (odor, amount, and appearance) of the discharge and body temperature. Severe metritis was characterized by a thin, watery, and reddish discharge; foul odor; a temperature >39"C; and feed refusal. Cows were given a 50% dextrose solution containing a broadspectrum antibiotic i.v. once daily until the temperature returned to normal. One additional treatment was administered after body temperature had returned t o normal, and cow body temperatures were monitored twice a day for 3 d following the last treatment. Subacute metritis was characterized by a thick, reddish yellow or white discharge. The cow was treated with 25 mg of PGF2, when diagnosed. If the cow had an elevated temperature (>39"C), she was treated as described for acute metritis. Subclinical metritis was characterized by a purulent discharge that was whitish yellow or reddish brown but accompanied by normal body temperature. Upon palpation, subclinical metritis was characterized by a thickwalled uterus and fluid that could be palpated within the uterine lining. The quantity, color, and odor of the discharge was noted daily. Cows with subclinical metritis were not treated unless body temperature was >39"C. If a body temperature >39"C was reached, Journal of Dairy Science Vol. 79, No. 12, 1996

cows were classified as having subacute metritis and were treated accordingly. Ovarian cysts were any fluid-filled structures >2.5 cm in size on the ovary that persisted >lo d. Ovarian cysts that were diagnosed <20 d postpartum were not treated but were scheduled for reexamination 2 wk later. Cows diagnosed with an ovarian cyst after 20 d postpartum were reexamined 10 d later. If the cyst persisted, the cow was treated simultaneously with 100 p g of GnRH (Cystorelin@;Sanofi Animal Health, Overland Park, KS) and 25 mg of PGFz,. All cows with ovarian cysts that had been treated were reexamined on the next herd check or within 2 wk. Cows with no parturient or postpartum reproductive disorders during the lactation were classified as healthy. Minor problems included dead calves ( a t birth or within 24 h ) , dystocia, retained placenta, or ovarian cysts that were not treated. Major problems consisted of cows with metritis or ovarian cysts that required veterinary intervention or treatment [modified from Oltenacu et al. (2311. Reproductively healthy cows were bred at the first observed estrus after 45 d postpartum. Most AI services (approximately 90%) were performed by one professional AI technician; the remaining AI were performed by the herd manager. All cows were bred at least once. To minimize uterine contamination, all AI pipettes were protected by a double sheath as they were passed through the vulva and vagina. Semen for 84 of the Holstein AI was from a common ejaculate; semen for 5 of the remaining AI was from a second collection date from the same high fertility bull. All Jerseys were bred from a common ejaculate of a high fertility bull. Cows that had not returned to estrus were checked for pregnancy at 45 d after AI. Days to first estimated ovulation were calculated from palpation records, estrus observations, and plasma progesterone concentrations. Ovulation occurred 1 d following an observed estrus, or, if estrus was not observed, ovulation was estimated to have occurred 5 d before an increase in basal progesterone that was >2 ng/ml. Observed estrus was defined as estrous behavior confirmed by a progesterone value <1ng/ml of plasma on the day of estrus with a subsequent increase over the next week. Unobserved estrus was determined by a progesterone value <1ng/ml of plasma with a subsequent increase over the next week unaccompanied by estrous behavior. An unconfirmed breeding was determined when the cow showed estrous behavior but progesterone values did not confirm the observation (>1ng/ml of progesterone), or when the timing of the AI was off by a day, or both. Four unconfirmed breedings were removed from

CRUDE PROTEIN AND REPRODUCTIVE PERFORMANCE

the analysis from primiparous cows fed the analysis (three (three from 13% 13% CP diet and one from a multiparous cow fed the 13% 13% CP diet). diet). Days to first AI service (DFS) (DFS) were monitored. Days open were the number of of days from calving to conception conception and were calculated only for the cows that were pregnant by 120 120 d postpartum. Services per conception (SC) were the total number of AI for cows conception ( SC) that conceived during the trial divided by the number of cows cows confirmed pregnant. First service conception rate (CRFS) (CRFS) was the percentage of cows that conceived on first AI. PR) AI. Cumulative Cumulative pregnancy rate ((PR) was the number of cows bred that became pregnant during the 120-d of cows 120-d trial divided by the number of bred. Statistical Statistical Analyses

Statistical Statistical analyses analyses were by least squares 2 x 2 x 2 factorial factorial analyses analyses using aa linear model on measured data (Models (Models [1] [l]and [2]) [21) or logistic transformation of categorical data (Model (Model [3]) [31) by SAS SAS (26): (26): Yijkl = IJ- + Pi + Lj + Bk + (PL)ij + (PB)ik + (LB )jk + (PLB )ijk + eijkl,

[1]

and and Yijklm = IJ+ + +

+ Pi + Lj + Bk + (PL)ij + (PB)ik (LB)jk + (PLB)ijk + Cl + D m + (PD)im (LD)jm + (BD)km + (PLD)ijm (PBD)ikm + (LBD)jkm + (PLBD)ijkm

+%~

~

where where IJ-p = overall mean of the population, population, Pi = mean effect effect of the the dietary dietary CP CP (i (i = = 13 13 or 20%), 20%), Lj Lj = = mean effect effect of of lactation lactation jj (first (first vs. vs. second or later), later), and Bk == mean mean effect effect of breed kk (Holstein (Holstein vs. vs. Jersey). Jersey). For Model = dependent variables Model [1], [ l l , Yijkl Yijkl= variables for for milk producproduction tion and and composition, composition, PUN, PUN, BW, BW, BCS, BCS, DFO, DFO, days days to first = first observed observed estrus estrus ( DFE), DFE), DFS, DFS, DO, DO, and SC; S c ; eijkl eijkl= random random residual, residual, assumed assumed to be N(O, N(0, s;l)' &). In Model Model [2], [2], Yijklm == dependent variable variable plasma In effect of cow cow 1,1, assumed assumed to be progesterone; Cl C1 == mean effect progesterone; N(0, sz2); and and D D,m == mean effect effect of day of pre-AI cycle cycle N (0, s;2); (d -5, or or 0). 0). ( d -21, -21, -15, -15, -10, -10, -5, Ynopq A, ++ LL,p ++ (FA)no (FA),, ++ (AL)op (AL),, ++ (FL)np (FL),, Y nopq == FF,n ++ An ++ (F AL)mno ++ eenopq [3] (FAL)mno [31 nopq

where Y YnOpq logistic transformation transformation of dependent where nopq == logistic variables, indicator indicator variables variables for for occurrence occurrence of health variables, disorders, CRFS, CRFS, and and PR; PR; FF,n == mean effect effect of dietary dietary disorders,

2229 2229

= 13 13 or 20%); 20%); A, An = mean mean effect effect of of lactation lactation o0 CP ((nn = Lp = = mean mean effect effect of of breed breed pp (first vs. second or later); L, e nopq == random random residual, residual, (Holstein vs. Jersey); and enopq 2 assumed N (0, se2). s;2)' [3] were modified for for analyses analyses of of Models [[1] l l and [31 reproductive measurements as a 2 xx 2 xx 2 xx 22 factorial factorial reproductive included an additional factor factor for for arrangement, which included reproductive health status (healthy cows cows and and cows cows reproductive with major major health health with minor problems vs. cows with problems) in the models. of treatments were considered considered to to be be differEffects of ent at P < 0.05. Effects were considered considered as as trends trends if if 0.05 < P < 0.10. Model [3] [3] effects were tested tested using using aa of fit. Main effects effects and and all all chi-square test for goodness of between the factors are are significant interactions between reported. analysis, based on the Cox Survival regression analysis, proportional hazard model, proportional h ( t ; Z1,. . ., z k ) = h o ( t ) exp(SBjXj),

[41

of variables and their their was used ttoo analyze the effects of [4], hh(t; Zl, .... = interactions with DO. In Model [4], ( t ; Z1, . .,, zZk) k) = hazard function of of DO, t, for cows with covariables covariables Xi, Xl, . . ., X,. ..., Xn. The covariables considered were health status, diet, diet, breed, lactation, lactation, and their interactions as tus, DFO, DFE, DFS, FCM, and BCS and BW well as DFO, changes. The factor h,(t) hoC t) = = baseline hazard function . , . = Zk = 0, and Bj = regression corresponding to Z1 Zl = ... coefficient of the covariable Xj. Xj' In our application, a hazard function approximated the conditional conditional probability that conception occurred during day t, given (21, 26). that conception had not occurred before t (21, Cows that did not conceive during the study were assigned the status of of censored aatt 120 DO. Only statistically significant covariables, main effects, or interactions were retained in the model. interactions RESULTS AND DISCUSSION

Among cows fed the low or high CP diets, Among diets, differences were not significant for age and lactation number at calving; BW and BCS at wk 1 1 postpartum; or milk, protein, or fat production from the previous (Table 1). 1).First lactation cows weighed less lactation (Table ( P < 0.05) than did second and had a higher BCS (P lactation or later cows at wk 11 postpartum. Holsteins weighed more than Jerseys at wk 11 postpartum and had higher milk and fat production in the previous (Table 1; 1; P < 0.05). 0.05). lactation (Table Production and Physiological Response Production

( P >> 0.10) 0.10) in mean milk There were no differences (P composition from wk 11to 15 15 of lactation production or composition Journal of Dairy Dairy Science Science Vol. 79, Journal 79, No. 12, 1996

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BARTON ET AL.

except for milk protein percentage among cows fed low or high CP diets (Table 4). When period (1 = wk 1 to 8; 2 = wk 9 to 15 of lactation) and cow were added to Model [l], there was an interaction of diet and period for production of milk and milk protein ( P < 0.05). Cows fed the 20% CP diet had higher milk production in period 1 than did cows fed the 13% CP diet (27.9 f 0.5 vs. 26.5 f 0.4 kg/d, respectively); production in period 2 was similar for cows fed the 20 and 13% CP diets (26.0 f 0.4 vs. 26.6 f 0.5 kg/d, respectively). Cows fed the 20% CP diet also had higher milk production in period 1 than did cows fed the 13% CP diet (0.89 _+ 0.01 vs. 0.82 k 0.01 kg/d, respectively); production in period 2 for cows fed the 20 and 13% CP diets were 0.86 k 0.01 vs. 0.81 k 0.01 kg/d, respectively. Milk production responses during this trial were similar to those reported by Carroll et al. ( 6 1 when experimental diets contained either 13 or 20% CP. Multiparous cows on this study had higher ( P < 0.05) production of milk, 4% FCM, fat, and protein but no difference in milk fat and protein percentages compared with those of primiparous cows (Table 4).Holstein cows produced more kilograms of milk, 4% FCM, and fat and with a lower percentage of milk protein and fat than did Jersey cows (Table 4; P < 0.05). There was an interaction ( P < 0.05) of

lactation number and breed on milk production and milk protein percentage. Mean values and change in BW and BCS from wk 1 to 15 postpartum were not affected by diet, lactation number, or breed (Table 4). Multiparous cows had significantly higher mean BW and tended toward a lower ( P < 0.10) mean BCS than did primiparous cows. Holstein cows had a higher mean BW than did Jersey cows (Table 4). There was a significant main effect on mean PUN concentration for wk 1 to 15 postpartum for diet, lactation, and breed (Table 4). The concentration of PUN was elevated in cows fed the 20% CP diet by 1 wk postpartum, increased until wk 4, and then was maintained throughout the experiment (Figure 1 ) . The PUN concentrations for low and high CP diets (8.6 and 21.0 mg/dl, respectively) on this study were slightly lower than those observed by Carroll et al. ( 6 ) and slightly higher than those observed by Jordan and Swanson (18). The concentrations of PUN for cows fed 20% CP rations have been reported to range from 15.4 mg/dl ( 1 2 ) to 29.2 mg/dl ( 3 ) . A significant effect of parity (first vs. second lactation or later) on PUN was observed. Upon review of the statistical analyses of PUN concentrations from a previous study, the authors found a difference between primiparous and multiparous cows (16.6 vs.

TABLE 4. Least squares means of main effect of diet, lactation, and breed on lactation performance and plasma urea N ( P U N ) concentration from wk 1 to 15 postpartum. CP Cow, no. Production Milk, kg/da 4% FCM, kgld ME1 4% FChI, kgld Milk fat, kgld Milk fat, % Milk protein, kg/d Milk protein, %a BW Mean,2 kg Change ( w k 1 to 151, kg BCS3 Mean4 Change (wk 1 to 1515 PUN, mgldlb

13%

20%

32

32

25.0 25.2 32.5 1.01 4.10 0.80 3.23

25.4 25.7 32.6 1.04 4.21 0.85 3.41

507 1.1 2.49 -0.26 8.6

508 2.4 2.55 -0.25 21.0

Lactation

P

0.7264 0.5827 0.9634 0.5397 0.3605 0.1160 0.0006

1

34

30

21.8 22.3 30.6 0.91 4.23 0.71 3.30

28.7 28.6 34.6 1.14 4.08 0.94 3.34

0.7863 501 0.9087 3.0 0.5402 0.9384 <0.0001

2.61 -0.20 14.0

aLactation by breed interaction ( P < 0.05). bDiet by breed interaction ( P < 0.05). 'Mature equivalent. Wovariantly adjusted with wk 1 BW. 3Body condition score on a five-point scale where 1 = thin to 5 = fat. 4Covariantly adjusted with wk 1 BCS. SBCS at wk 15 are the means of wk 15 and 17. Journal of Dairy Science Vol. 79, No. 12, 1996

22

514 0.47 2.43 -0.31 15.6

Breed

P

<0.0001 <0.0001 0.0148 <0.0001 0.1790 <0.0001 0.4326

Holstein Jersey 47

17

29.4 27.9 38.1 1.07 3.69 0.89 3.05

21.1 23.1 27.1 0.97 4.61 0.76 3.59

0.0158 528 0.8212 4.4 0.0880 0.5389 <0.0105

2.55 -0.14 13.7

487 -0.87 2.49 -0.37 15.8

P

SEM

<0.0001 0.5 <0.0001 0.5 <0.0001 0.0451 <0.0001 0.2173 <0.0001

0.02 0.05 0.01 0.02

<0.0001 2 0.6432 4.7 0.5090 0.04 0.9138 0.07 0.0006 0.26

2231

CRUDE PROTEIN AND REPRODUCTIVE PERFORMANCE

TABLE 5. Least squares means of main effect of diet, lactation, and breed on reproductive performance and plasma urea N ( P U N ) concentration of cows. CP ~

~

Lactation

Breed

13%

20%

P

1

22

P

Holstein

Jersey

P

SE31

23.2

25.8

0.2615

25.7

23.3

0.2855

26.8

22.1

0.0407

1.0

41.4 62.5 71.4 1.70

39.5 59.9 80.7 1.75

0.7492 0.5867 0.1072 0.8272

44.9 62.0 67.3 1.52

36.1 60.4 84.8 1.93

0.1386 0.7230 0.0033 0.0421

42.4 61.7 74.2 1.69

38.5 60.7 77.9 1.75

0.5086 0.8410 0.5231 0.7564

2.5 2.0 2.5 0.08

40.6

43.7

0.6095

61.7

20.0

0.0274

44.7

35.3

0.8708

75.0

87.5

0.3960

79.4

83.3

0.7510

78.7

88.2

0.6932

8.5

22.1

<0.0001

14.0

16.5

0.0072

14.4

16.0

0.1124

~

Days to first estimated ovulation Days to first observed estrus Days to first AI Days open Services per conception Conception rate at first AI service, %a Cumulative pregnancy rate, % PUN a t First AI service, mg/dla

0.4

"Diet by breed interaction ( P < 0.05).

17.9 mg/dl; P < 0.05) ( 6 ) . Peterson and Waldern ( 2 4 ) reported an increase in blood urea N as age of cows increased (range, 2 to 12.5 yr). Kaim et al. ( 1 9 ) reported that lactation number (second and third vs. fourth or later lactation) did not influence blood urea

values were similar between the breeds. This interaction may reflect the differential between protein intake and protein utilization for lactation between the two breeds.

N.

Reproductive Health and Performance

A significant main effect of breed was not reported The efficiency of reproductive performance, as by Carroll et al. ( 6 1 for Jerseys and Guernseys versus monitored by DFO, DFE, DFS, SC, CRFS, and PR, Holsteins or by Howard et al. ( 1 7 ) for Ayrshires was not influenced by dietary CP concentration versus Holsteins. In this study, there was an inter- (Table 5). Cows fed the 20% CP diet had numerically action between diet and breed for mean PUN concen- more DO than did cows fed the 13% CP diet ( P = tration ( P< 0.05; Table 4;Figure 1 ) . With the 20% 0.1072). CP diet, Jerseys had a higher PUN concentration The higher CP diet increased DO, which is similar than did Holsteins, but, with the 13% C P diet, PUN to results of other studies that have compared high

30

'ijj

25

E

20

5 a

1

1 a?

i

$

1

$

CI

6

$

15

M

L

i 3 10

4

a

-5

ii

a

s L 2

5

a

0

0

2

4

6

8

10

12

14

Week postpartum

Figure 1. Plasma urea N concentrations of Jersey (open symb o k ) and Holstein (closed symbols) cows fed a 13% ( 0, 0 ) or 20% ( 0 , m) CP diet.

-22

-20

-18

-16

-14

-12

-10

-8

-6

-4

-2

0

Time prior to first AI service, d

Figure 2. Plasma progesterone concentrations prior to first AI (day 0 ) of first (closed symbols) and second or later lactation (open symbols) cows fed a 13% ( 0 , or 20% ( 2 ,W ) CP diet. Journal of Dairy Science Vol 79, No. 12, 1996

2232

BARTON ET AL.

TABLE 6. Means of main effect of diet, lactation, and breed on plasma progesterone concentrations for d -21, -15, -10, and -5 prior t o first AI service.' CP

Cow, no. Plasma progesterone, ng/ml d -21 d -15 d -10 d -5 d 0 (AI service)

Breed

Lactationa

13%

20%

1

22

Holstein

Jersey

32

32

34

30

47

17

1.1 4.5 6.5 5.3 0.5

1.2 4.8 6.9 5.5 0.2

0.9 4.0 6.0 5.0 0.4

1.4 5.3 7.5 5.9 0.3

1.4 4.4 6.4 5.2 0.4

0.6 5.2 7.5 5.9 0.3

aTrend toward lactation main effect ( P < 0.10). 'Standard error of the mean = 0.14.

and low CP diets (13, 18, 19). Howard et al. ( 1 7 ) fed cows either a 15 or 205% CP diet and managed them with a controlled program of bull fertility, estrus detection, and reproductive health; 17 reproductively unhealthy cows were removed from the study. The overall results ( 1 . 4 SC and 80 D O ) for those two treatment groups were similar to the overall results of the present study ( 1 . 7 SC and 76.1 DO). Carroll et al. ( 6 ) fed either a 13 or 20% CP diet, which resulted in an SC of 1.5 and 1.8 and a DO interval of 72 and 82, respectively. Those results were similar to results of the present study (Table 5). Cows fed the 20% CP diet had a significantly higher PUN concentration at first AI service than did

cows fed the 13% CP diet (Table 5). Plasma urea N for the 20% CP treatment was higher than the 20.0 mg/dl value that was reported by Ferguson et al. ( 1 1 ) to have a negative impact on reproductive performance of early lactation dairy cows. The PUN concentrations in this experiment for cows fed the 20% CP diet were also higher than the 16 mg/dl value reported by Elrod and Butler ( 8 ) to reduce fertility in heifers. The only main effect of breed on reproductive performance was a shorter ( P < 0.05) DFO interval for Jersey cows than for Holstein cows. There was an interaction ( P < 0.05) between diet and breed for both CRFS and PUN at first AI service. As with mean

TABLE 7. Occurrence and classification of reproductive disorders by diet, lactation, and breed. CP

Cow, no Summary' Healthy Minor problems Major problems Reproductive disorder2 Retained placenta Calf death Dystocia score ( > 2 ) 3 Ovarian cyst Untreated Treated Metritis, treated

Lactation

Breed

13%

20%

1

22

Holstein

Jersey

32

32

34

30

47

17

18 3 11

8

9 15

15 5 14

11 7 12

17 9 21

9 3 5

3 3 5

3 2 5

6 4 7

0 0

10 6 11

4 4 12

9 6 19a

3 5

0

Ob

a2bMeans with different superscripts differ ( P < 0.05). IHealthy = Cows with no reproductive health problems during lactation, minor problems = cows with minor health problems (untreated ovarian cysts, nonsystemic metritis, retained placenta, or dystocia), and major problems = cows with major health problems (treated ovarian cysts o r systemic metritis) that required veterinary assistance or treatment. Cows are posted in only one category. Wows with multiple disorders are posted in more than one category. 3Dystocia score: 1 = no problem, 2 = slight problem, 3 = needed assistance, 4 = considerable force, and 5 = extreme difficulty. Journal of Dairy Science Vol. 79, No. 12, 1996

2233

CRUDE PROTEIN AND REPRODUCTIVE PERFORMANCE

PUN concentrations for wk 1 to 15, Jerseys had higher PUN concentrations than did Holsteins fed the high CP diet, but PUN concentrations were similar for cows fed low CP diets. The CRFS were lower for Holstein cows than for Jersey cows when fed the low CP diet (38.1% vs. 83.3%, respectively) and higher for Holstein cows than for Jersey cows when fed the high CP diet (61.9% vs. 16.7%, respectively). Lactation number had a main effect ( P < 0.05) on DO, SC, CRFS, and PUN concentration at first AI service. Multiparous cows were open 17.5 d longer, required 0.42 more SC, and had higher PUN concentrations at first AI service than first lactation cows (Table 5 ) . The CRFS was 20% for older cows, and 61.7% for first lactation cows. There were no interactions of diet by lactation number on reproductive performance during this study. Kaim et al. ( 1 9 ) reported that high CP diets reduced conception rates of cows in fourth or later lactation, but had no effect on second and third lactation cows. Bruckental et al. ( 3 ) reported that primiparous cows and cows in fourth lactation or later had lower 16-wk PR than second or third lactation cows when fed rations containing different protein percentages or varying protein sources. Canfield et al. ( 5 ) reported a decrease in conception rates for cows fed high CP diets, regardless of parity (primiparous vs. multiparous). There were no significant interactions of diet or breed by day prior to first AI on plasma progesterone concentration (Table 6 ) . There was an interaction of diet, lactation, and day on progesterone concentration ( P < 0.05; Figure 2). Cows in second or later lactation

fed the 13% C P diet had a higher concentration of plasma progesterone on d -15, -10, and -5 of the estrous cycle prior to first AI service than did first lactation cows fed the 13% C P diet. Cows in second or later lactation fed the 20%' C P diet had a pattern of plasma progesterone profiles that was similar to that for first lactation cows fed the high CP diet (Figure 2). No interactions existed between diet and lactation number for DFO, DFE, or DFS, so the explanation for this interaction is not clear. The occurrence and classification of parturient and postpartum reproductive disorders are reported in Table 7. There were no main effects or interactions among diet, breed, and lactation number on reproductive health status. Overall, 40.6% of the cows were healthy, 18.8% had minor health problems, and 40.6% experienced major health problems. The only significant difference for the occurrence of reproductive disorders was a breed effect (Table 7). Holsteins had a 40% occurrence of metritis that required treatment, but no metritis cases were reported for Jersey cows. Approximately 30% of the cows had systemic metritis that was treated, 9% had retained placenta, 19% had ovarian cysts that were not treated, and 17% had ovarian cysts requiring treatment. The health status of the cows (healthy or major problem) was added to the ANOVA model. When variation caused by health status was analyzed, two measurements became trends (Table 5 ) . Cows fed the 13% C P diet had lower DFO than did cows fed the 20% CP diet (21.5 k 2.0 vs. 25.6 1.6; P = 0.0954). This result was similar to a trend reported by Carroll

*

TABLE 8. Least squares means of health status on reproductive performance.'

Days to first estimated ovulation Days to first observed estrus Days to first AI service Days open Services per conception Conception rate at first AI service, % ' Cumulative pregnancy rate, % PUN4 a t first AI service, mg/dl

Healthy o r minor uroblemz

Major uroblem3

P

SEM

25.2 37.7 58.7 71.9 1.68

21.9 51.2 68.4 84.1 1.65

0.2307 0.0405 0.0697 0.1042 0.8789

1.0 2.3 2.0 2.5 0.09

48.9

26.3

0.3103

88.9

63.2

0.0601

14.9

15.2

0.8264

0.42

'Analysis included diet, lactation, breed, health status, and their interactions in the statistical model. 'Cows with no health problems or minor health problems (untreated ovarian cysts, retained placenta, or dystocia) during lactation. 3Cows with major health problems (ovarian cysts or metritis) that required veterinary assistance or treatment. 4Plasma urea N. Journal of Dairy Science Vol. 79, No. 12, 1996

2234

BARTON ET AL

et al. ( 6 ) . Also, first lactation cows ovulated sooner than did cows in second or later lactation (21.3 f 1.8 VS. 25.8 f 1.8; P = 0.0626). The impact of health status on reproductive performance is depicted in Table 8. Results for healthy cows and for cows with minor problems were combined because few cows had minor health problems. Healthy cows and cows with major health problems had similar reproductive efficiencies, except for DFE. Healthy cows were detected in estrus 13.5 d earlier than cows with major problems. Healthier cows were pregnant 12.2 d earlier, had a higher CRFS, and had a higher PR than unhealthy cows, but these differences were not significant (Table 8 ) . These tendencies were probably due to good management, includ-

Low CP (13%)

A

0

. 10

. 20

. 30

. 40

. 50

. 60

70

.

.

80

90

.

.

.

.

100 110 120 130

Postpartum, d

B

High CP (20%)

ing early detection of disorders, timely treatment, and subsequent monitoring for the efficacy of treatment. Galton et al. ( 1 4 ) reported that herds with a defined program for herd health had improved reproductive performance than other herds because of fewer SC, DFS, and DO. Galton et al. ( 1 4 1 attributed these improvements in reproductive performance to routine genital examinations, early detection of reproductive abnormalities, veterinary information and therapy, methods of detection of estrus, and management awareness of the reproductive status of cows in the herd health program. The economic value and health benefits of a preventive program designed to maintain healthy cows has been well established (4,16). This approach to reproductive health management lessens the impact of disorders on overall reproductive efficiency. Results of survival analysis of DO are reported in Table 9 and Figure 3. Twelve cows did not conceive during this trial; 8 were fed a low CP diet, and 4 were fed a high CP diet. These cows were excluded from the factorial analysis of DO presented in Tables 5 and 8. Days to first AI service was a significant factor in predicting DO. The negative coefficient (Table 9 1 from Model [41 indicates that, as DFS increases, the conception rate decreases. The positive regression coefficient and corresponding proportional hazard ratio for diet indicated that cows fed a high CP diet were nearly twice as likely to conceive over the next given period than were cows fed a low CP diet. Health status was not significant, but there was a trend toward a n interaction between diet and health status. In Figure 3A, cows fed the low CP diet had no difference in median DO, regardless of health status (77.5 vs. 85 d, healthy vs. major health problems, respectively). In Figure 3B, cows fed the high CP diet had a difference of 48 median DO (64 vs. 112 d, healthy vs. major health problems, respectively). Therefore, in

TABLE 9. Regression coefficients and hazard ratios from survival analysis on days open.' Variable

0

10

20

30

40

50

60

70

80

90 100 110 120 130

Postpartum, d

Figure 3 . Estimated cumulative r i t e s of conception for cows fed a 134 (A; 0 , e) or 20% ( B ; 0, CP diet for cows that were either healthy (closed symbols) or experienced a major health problem during lactation (open symbols). The days to first AI variable was fixed a t 60 d ( X I = 60 in the proportional hazard model, Model [4]). Journal of Dairy Science Vol. 79, No. 12, 1996

Days to first AI, X, Diet X, = 0 for 13V CP X, = 1 for 20% CP Health status X, = 0 for healthy o r minor problems X, = 1 for major problems Diet by health status interaction

x4 = x:, x x:,

'According to Model [41

Hazard Coefficient ratio P -0.038741

0.962

0.0040

0.674253

1.963

0.0403

-0.285591

0.752

0.6140

-1.346661

0.260

0.0680

CRUDE PROTEIN AND REPRODUCTIVE PERFORMANCE

this study, high C P diets tended to increase DO when cows had major health problems; otherwise, a high CP diet decreased DO. Several hypotheses have been proposed to explain how high CP diets may reduce reproductive efficiency of dairy cows (6, 11, 28). Elevated concentrations of ammonia, urea, or other toxic by-products of N metabolism may negatively impact the reactivity of lymphocytes ( 6 , 11). As a result, the ability of the cow to respond t o an antigenic stressor during the postpartum period might have been reduced. Cows fed the high CP diet might have experienced suppression of their immune system that could have had a negative impact on their health status and reproductive efficiency. CONCLUSIONS

In this study, PUN concentrations were significantly different because of diet, lactation, and breed. Days to first estimated ovulation were significantly affected by breed. When health status was added to the statistical model, there was a trend toward differences for diet and lactation. Days to first observed estrus, DFS, and PR were significantly influenced by health status; SC and CRFS were significantly influenced by lactation number. Survival regression analysis showed an interaction between CP concentration in the diet and health status when DFS was included in the model. When fed the high CP diet, healthy cows had lower median DO than did cows that experienced a major health problem. When the low CP diet was fed, no statistical difference was detected in the median DO between healthy cows and those with major health problems. Within the current study, implementation of a strict program of reproductive management allowed goals of high reproductive efficiency to be achieved regardless of PUN concentrations. ACKNOWLEDGMENTS

The authors thank Colleen Vallee, Kathy Hamilton, Kevin Tobey, and Kathy Dellapi for their assistance with sample collection. Appreciation is also extended to Ann Chase, Farm Manager, and J. Franklin Witter Animal Science Center staff, for their assistance during the trial. Statistical analysis support was from William Halteman, University of Maine, and Dave R. Thomas, Oregon State University. Federated Genetics (Lancaster, PA) contributed a portion of the semen.

2235

REFERENCES 1Association of Official Analytical Chemists. 1980. Official Methods of Analysis. Vol. I. 13th ed. AOAC, Washington, DC. 2Barton, B. A., and D. J. Carroll. 1992. Dietary crude protein and reproductive efficiency in dairy cows: considerations when designing or evaluating research protocols. Page 21 in Proc. 27th Annu. Pacific Northwest h i m . Nutr. Conf., October 20-22, 1992, Spokane, WA. Washington State Univ., Pullman. 3Bruckenta1, I., D. Dori, M. Kaim, H. Lehrer, and Y. Folman. 1989. Effects of source and level of protein on milk yield and reproductive performance of high-producing primiparous and multiparous dairy cows. Anim. Prod. 48:319. 4Cal1, E. P., and J. S . Stevenson. 1985. Current challenges in reproductive management. J Dairy Sci. 68:2799. 5 Canfield, R. W., C. J. Sniffen, and W. R. Butler. 1990. Effects of excess degradable protein on postpartum reproduction and energy balance in dairy cattle. J. Dairy Sci. 73:2342. 6 Carroll, D. J., B. A. Barton, G. W. Anderson, and R. D. Smith. 1988. Influence of protein intake and feeding strategy on reproductive performance of dairy cows. J. Dairy Sci. 71:3470. 7Dewar, W. A., and P. McDonald. 1961. Determination of dry matter in silage by distillation with toluene. J. Sci. Food Agric. 12:790. 8 Elrod, C. C., and W. R. Butler. 1993. Reduction of fertility and alteration of uterine pH in heifers fed excess ruminally degradable protein. J. Anim. Sci. 71:694. 9Ferguson, J. D., T. L. Blanchard, D. Hoshall, and W. Chalupa. 1986. High rumen degradable protein as a possible cause of infertility in a dairy herd. J . Dairy Sci. 69(Suppl. 1):120. (Abstr.) lOFerguson, J. D., and W. Chalupa. 1989. Impact of protein nutrition on reproduction in dairy cows. J. Dairy Sci. 72:746. 11Ferguson, J . D., D. T. Galligan, T. Blanchard, and M. Reeves. 1993. Serum urea nitrogen and conception rate: the usefulness of test information. J. Dairy Sci. 76:3742. 12Folman, T., H. Newmark, M. Kaim, and W. Kaufmann. 1981. Performance, rumen and blood metabolites in high yielding cows fed varying protein percents and protected soybean. J. Dairy Sci. 64:759. 13 Folman, Y., M.Rosenberg, Z. Herz, and M. Davidson. 1973. The relationship between plasma progesterone concentration and conception in postpartum dairy cows maintained on two levels of nutrition. J. Reprod. Fertil. 34:267. 14 Galton, D. M., H. L. Barr, and L. E. Heider. 1976. Effects of a herd health program on reproductive performance of dairy cows. J. Dairy Sci. 60:1117. 15 Garcia-Bojalil, C. M., C. R. Staples, W. W. Thatcher, and M. Drost. 1994. Protein intake and development of ovarian follicles and embryos of superovulated nonlactating dairy cows. J. Dairy Sci. 77:2537. 16Heider, L. E., D. M. Galton, and H. L. Barr. 1980. Dairy herd reproductive health programs compared with traditional practices. J. AVMA (J. Am. Vet. Med. Assoc.) 176:743. 17Howard, H. J., E. P. Aalseth, G. D. Adams, L. J. Bush, R. W. McNew, and L. J. Dawson. 1987. Influence of dietary protein on reproductive performance of dairy cows. J. Dairy Sci. 70:1563. 18 Jordan, E. R., and L. V. Swanson. 1979. Effect of crude protein on reproductive efficiency, serum total protein, and albumin in the high-producing dairy cow. J . Dairy Sci. 62:58. 19 Kaim, M., Y. Folman, H. Newmark, and W. Kaufman. 1983. The effect of protein intake and lactation number on post-partum body weight and reproductive performance of dairy cows. Anim. Prod. 37:229. 20 Krishnamoorthy, U,, T. V. Muscato, C. J. Sniffen, and P. J. Van Soest. 1982. Nitrogen fractions in selected feedstuffs. J. Dairy Sci. 65:217. 21Lee, L. A., J. D. Ferguson, and D. T. Galligan. 1989. Effect of diseases on days open assessed by survival analysis. J . Dairy Sci. 72:1020. 22 National Research Council. 1989. Nutrient Requirements of Dairy Cattle. 6th rev. ed. Natl. Acad. Sci., Washington, DC. Journal of Dairy Science Vol. 79, No. 12, 1996

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23 Oltenacu, P. A., J . H. Britt, R. K. Braun, and R. W. hlellenberger. 1984. Effect of health status on culling and reproductive performance of Holstein cows. J. Dairy Sci. 67:1783. 24 Peterson, R. G., and D. E. Waldern. 1981. Repeatabilities of serum constituents in Holstein-Friesians affected by feeding, age, lactation. and pregnancy. J. Dairy Sci. 64:822. 25 Robertson, J. B., and P. J. Van Soest. 1981. The detergent system of analysis and its application t o human foods. Page 123 in The Analysis of Dietary Fibers in Foods. W.P.T. James and 0. Theander, ed. Marcel Dekker, New York, NY. 26 SASB Technical Report P-229, SAWSTAT@Software: Changes and Enhancements, Release 6.07 ed. 1992. SAS Inst., Inc., Cary, NC.

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27 Smith, R. D. 1985. Factors affecting conception rate. Fact Sheet IRh4-10 in Dairy Integrated Reproductive Management. E. R. Jordan, ed. Reproductive Management Mimeo Ser. No. 87, Corne11 Univ. Coop. Ext., Ithaca, NY. 28Staples, C. R., C. Garcia-Bojalil, B. S. Oldick, W. W. Thatcher, and C. A. Risco. 1993. Protein intake and reproductive performance of dairy cows: a review, a suggested mechanism, and blood and milk urea measurements. Page 37 in Proc. 4th Annu. Florida Ruminant Nutr. Symp., Gainesville, Florida. Univ. Florida, Gainesville. 29Wildman, E. E., G. M. Jones, P. E. Wagner, R. L. Boman, H. F. Troutt, J r . , and T. N. Lesch. 1982. A dairy cow body condition scoring system and its relationship to selected production characteristics. J. Dairy Sci. 65:495.