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Epidemiological study on factors influencing fertility indices in Israeli dairy herds
fheriogenology38:385-405,1992
EPIDEMIOLOGICAL STUDY ON FACTORS INFLUENCING FERTILITY INDICES IN ISRAELI DAIRY HERDS G. Frances,’
0. Distl:
H. Krau131ich2 and E. Mayer?
‘Hahaklait Clinical Veterinary Services, P.O.B. 9610 Haifa, Israel ‘Institut fur Tierzucht und Tierhygiene der Universitat Miinchen VeterinarstraBe 13, 8000 Miinchen 22, FRG 31nstitute for Veterinary Clinical and EpidemioIogical Research P.O.B. 9610, Haifa, Israel Received
for publication: April 3, 1991 Accepted: JUZ~ 12, 2992 ABSTRACT
The objective of this study was to determine feeding factors connected with differences in the fertility of Israeli Kibbutz dairy herds. In an epidemiological case-control survey, data from 30, low-fertility Kibbutz dairy herds having a mean overall conception rate of 35% in multiparous cows were compared with the data from 30, high-fertility Kibbutz dairy herds having a mean overall conception rate of 48% in multiparous cows. Nutritional factors accounted for 67% of the differences between low-fertility and high-fertility herds in the overall conception rate of multiparous cows, while only 4.8% could be related to the body condition during the dry period. Among the factors which occurred more frequently in the low-fertility than in the high-fertility herds were 1) a higher average protein density and lower energy/protein ratio was fed during lactation and 2) a single feeding group was maintained for all lactating cows. 3) There were phytoestrogens in the silage or alfalfa hay, fed during lactation. 4) Faulty dry period was instituted, which was defined as the presence of at least one of the following three practices: a) the daily feed was above 3 kg of high lactation mix; b) more than 15 Meal of net energy per day was given during the first part of the dry period; c) more than 30% of the cows were obese during the dry period. Three or more risk factors were found in one high-fertility herd and in 20 low-fertility herds. This finding emphasizes the importance of identifying and removing risk factors as a possible means for improving the reproductive performance of herds. Key words: epidemiological
study, fertility, dairy cattle, nutrition
Acknowledgments This study was supported by a grant from the Research Fund of the Israeli Milk Marketing Board and the Israeli Cattle Breeders’ Association, Tel Aviv. The authors thank D. Avieli, M. Ben Meir, Dr. 0. Nir and D. Peri for their help as well as the veterinarians and staffs of the herds used in this study.
Copyright 0 1992 Butterworth-Heinemann
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INTRODUCTION The aim of our investigation was to determine the factors which influence herd fertility levels in Israeli Kibbutz dairy herds. These were commercial dairy herds with an average of 300 cows yielding an average milk yield of 8,000 to 11,000 kg per year. In spite of apparently similar management systems, an uniform genetic background and a similar pattern of veterinary and insemination services, the differences in fertility indices between the herds were considerable. To identify the factors related to differences in reproductive performance we undertook a wide-scale epidemiological study of low- and high-fertility herds. MATERIALS
AND METHODS
Sixty Kibbutz herds with 18,900 dairy cows were included in this study. The herds were selected according to the data on overall conception rate, which was derived from herd book records. The overall conception rate was calculated as the percentage of the number of multiparous cows with conceptions divided by the number of inseminations performed in all multiparous cows, regardless of whether or not pregnancy was established. Thirty herds, having an overall conception rate of more than 45% among cows from the second and subsequent lactations during the months of November to June, were classified as high-fertility herds. The remaining 30 herds with an overall conception rate of less than 40% the same period were classified as low-fertility herds. Selection on the basis of overall conception rates in the autumn-spring months was intended to eliminate the influence of the hot summer period. The number of cows in the surveyed herds varied from 235 to 460 head; the average yearly milk production of the cows from the second lactation and onwards varied from 8,100 to 11,000 kg. The herds were located all over the country with the exception of the Jordan Valley and the Southern Negev (desert) regions. Each herd was visited one or two times from July 1987 to January 1989. The following reproductive indices of primiparous and multiparous cows were recorded: 1) days from calving to the first insemination; 2) days from the first to the last insemination (wasted days); 3) days from calving to conception (days open); 4) average yearly milk yield (based on herd records); 5) incidence of reproductive disorders based on data derived from either local veterinary records or from records of the Israeli Herd Book and 6) herd incidence of postpartum anestrus if occurrence was above 25%. The postpartum anestrus was defined as no observable estrous behaviour prior to 60 days postpartum and no other reproductive disorder noted until 60 days postpartum. The percentage of herds with a
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387
high incidence of post-insemination anestrus was calculated using the incidence of cows being diagnosed not pregnant by palpation per rectum at 40 to 50 days after insemination. The cutoff point for herds classified as high incidence post-insemination anestrus was 22%. Detailed data on the allocation of each herd to nutritional groups as well as the food components and the exact feeding schemes of these groups were recorded. The nutritional values of the concentrate foods were calculated from the producer’s analysis or from national tables; roughage values were determined from laboratory data based on the examination of the samples sent by herd managers or by the investigators. The following feed factors were recorded: 1) the dry matter content of ration fed to high and low milk producing cows and average dry matter intake during the entire lactation; 2) parallel data were recorded on net energy per kilogram of dry matter; 3) the percentage of protein and 4) the percentage of roughage. Data on the feeding regimens during the dry period, which generally lasted 8 weeks, were recorded separately for the first 5 to 6 weeks of the dry period and for the final 2 to 3 weeks. The following data were included: 1) total dry matter intake; 2) net energy intake; 3) protein intake and 4) the mix, silage and hay intake during each of those periods. Additional factors connected with nutrition were the feeding of distiller grains during lactation, the feeding of whey during the lactation, the use of self loading cart with attached rotating knife for cutting silage (self-cutting-cart) for the preparation and distribution of mix, the examination of roughage for fungi contamination and for phytoestrogens and the examination of silage bunkers. Most samples of herd silage and occasional hay samples were sent mycotic examination. In the 25 herds in which hyperestrogenic activity was ted, forage samples were sent out for examination of phytoestrogen levels The mycotic and phytoestrogen examinations were performed at the Veterinary Institute, Beit Dagan, Israel.
out for suspecas well. Kimron
Body condition was scored on a scale of 1 to 5 and was assessed for dry cows and nulliparous heifers in the last 2 months of gestation. Additional data were recorded on instances of observed estrous and the type of housing in which the animals were maintained.
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Statistical
Methods
Fertility indices, nutrition and management factors, based on herd averages, were tested on significant differences between low-fertility herds and high-fertility herds using the following linear least-square model (Model 1): yijW
Yijkl Ei,bj Mi Fj HC, eijW
=
: : : : : : :
/J + bt Mi + bj Fj + HC, + eyu; dependent variable (fertility index or nutritional factor of the ijkl-th herd) model-dependent constant individual linear regression coefficients for Mi and Fj, respectively yearly average milk yield of herdij, yearly average percentage of fat of herd,ju herd class low-fertility herds or high-fertility herds remaining factors
Variance explained by nutritional linear least-square model (Model 2): Yij yij
b”. ii
eij
factors was quantified
by the following
= p + Zb& + eij; : dependent variable of the ij-th herd : model-dependent constant : individual linear regression coefficients for effects included in & : the following nutritional factors were regarded simultaneously as individual effects in the model: intake of dry matter, net energy, protein, and roughage during lactation in all cows and in high producing cows; feeding regimen in the dry period (intake of dry matter, net energy, protein, mix, silage and hay); feeding of distiller grains during lactation; feeding of whey during lactation; division into feeding groups; use of a self-cuttingcart for preparation and distribution of feed mix, phytoestrogenic activity of roughage/silage; and examination results of silage bunkers (i = 1 to 20) : remaining factors
A similar model was applied to analyze the effect of body condition during the dry period on milk production and on reproductive indices and disorders. In this model only the effect of body condition score during the dry period was regarded as an independent variable (Model 3): Yij yij
bi BC, eii
= : : :
p + bi BC, + eij; milk production or reproductive index or disorder of the ij-th herd linear regression coefficient average body condition score of dry cows or nulliparous heifers in the last 2 months of gestation of the ij-th herd : remaining factors
Theriogenology
Variance the goodness R2 = R (X) = b x Y’Y
: : :
explained by the different models (R’) was used as a measure of fit by the model applied and was computed as follows:
of
R (X) / Y’Y = b’X’Xb / Y’Y, b’X’Xb: reduction in sum of squares corrected for mean by the model applied solution vector model-dependent design matrix total variance of the dependent variable Y corrected for the mean
The multiple correlation coefficient (r,) was estimated as the product moment correlation between the observed Y and the predicted Y and was calculated as the square root of R’.
RESULTS Milk Yield Fat corrected milk values were similar in both groups of herds, but the lowfertility herds had significantly higher milk production averages and significantly lower fat percentage averages in comparison with the high-fertility herds (Table 1). Overall Conception
Rate
Nulliparous heifers had the highest overall conception rate, while multiparous cows had the lowest. The differences in the overall conception rates between parity groups are a feature of Israeli dairy herds. The overall conception rate of nulliparous, primiparous and multiparous in high-fertility herds was significantly higher than the overall conception rate of the corresponding parity group in the low-fertility herds (Table 2). It appears that the factors impairing fertility levels affect all parity groups in low-fertility herds (Table 2). In high-fertility herds the correlation between the overall conception rate of primiparous and multiparous cows was significantly different from zero (r = 0.563); the corresponding coefficient of correlation in low-fertility herds was much lower (r = 0.282) (Table 3). The correlations between the overall conception rate of nulliparous cows and of the cows were in the range from -0.273 to 0.299 (Table 3).
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Table
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1. Average yearly milk yield in 30 herds with high and 30 herds with low overall conception rate Overall conception < 40%
rate > 45%
Significance
Milk yield (kg) Primiparous Multiparous
cows cows
9267 ” 112 10091 * 137
cows cows
3.08 + 0.04 3.06 + 0.04
8918 9773
2 112 + 137
0.0316 0.1066
Fat (%) Primiparous Multiparous Fat corrected Primiparous Multiparous
3.22 k 0.04 3.19 2 0.04
0.0057 0.0237
milk yield (kg) cows cows
7985 8667
+ 110 + 135
7882 8580
2 110 r 135
0.5145 0.6484
Days from Calving to the First Insemination The number of days to the first insemination was similar in both herds of primiparous animals. Multiparous cows in the low-fertility herds had a significantly (P = 0.006) shorter period to the first insemination than cows in high-fertility herds. It appears that this difference was strongly influenced by the efforts of the managers of low-fertility herds in order to compensate for the delay in conception by early insemination (Table 2). Wasted Days (Days Between
the First and Last Insemination)
There were significantly fewer wasted days (P < 0.001) in high-fertility herds than in low-fertility herds, with 18.6 days for primiparous cows and 24.6 days for multiparous cows (Table 2). A high incidence of negative pregnancy diagnoses in low-fertility herds contributed to the difference (Table 2). Days Open (Days from Calving to Conception) Fewer days to conception were recorded fertility herds with 5.5 days for primiparous cows (Table 2).
for high-fertility herds than for lowcows and 9.6 days for multiparous
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Table 2. Reproductive indices in dairy herds with high (n=30) overall conception rate (Model 1)
Overall conception
rate >45%
< 40%
and low (n=30)
Sienificance
Overall conception rate (%) Nulliparous Primiparous Multiparous
heifers cows cows
55.4 k 9.2 42.0 -+ 1.3 35.1 + 0.6
63.8 + 7.1 52.3 + 1.3 48.1 + 0.6
0.0001 0.0001 0.0001
Days from calving to the first insemination Primiparous Multiparous
cows cows
84.3 -+ 2.1 73.9 ?I 1.2
85.2 + 1.9 80.4 +- 1.1
0.7783 0.0006
cows cows
51.7 * 3.1 61.7 + 2.9
32.3 + 2.7 37.1 + 2.6
0.0001 0.0001
cows cows
125.5 2 3.3 120.3 k 3.6
120.0 2 3.0 110.7 f 3.3
0.2539 0.0708
Days from the first to the last insemination Primiparous Multiparous Days open Primiparous Multiparous
Number of daily scheduled observations of estrus
1.94 k 0.15
2.16 + 0.15
0.2969
High incidence of postpartum anestrus (% of herds) Primiparous Multiparous
cows cows
30.6 -+ 8.0 28.6 + 8.4
11.4 f 20.0 +
7.7 8.1
0.1069 0.4776
5.8 r 10.3 +
7.1 7.6
0.0022 0.0009
High incidence of postinsemination anestrus (% of herds) Primiparous Multiparous
cows cows
40.2 ;t 49.7 r
7.3 7.8
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392 Percentage
of Herds with High Incidence
Postpartum
Anestrus
The difference in the percentage of the herds with a high incidence (above 25%) postpartum anestrus between the two groups of herds was not significant (Table 2); however, the percentage of herds with a high incidence of post-insemination anestrus was higher in low-fertility than in high-fertility herds (Table 2). Percentage
of Herds with High Incidence
Post-Insemination
anestrus
The percentage of primiparous herds with a high incidence (above 22%) of post-insemination anestrus (negative per rectum pregnancy examination) in lowfertility herds and high-fertility herds was 40.2 and 5.8%, respectively (P < 0.01). In multiparous herds the corresponding values were 49.7 and 10.3%, respectively (P < 0.001; Table 2). Thus it appears that the occurrence of a high incidence of post-insemination anestrus is one of the primary factors influencing a low overall conception rate in a herd. Table 3. Correlations primiparous
between the overall conception rate of nulliparous heifers, and multiparous cows in herds with high and low fertility
Primiparous
cows
Multiparous
cows
Low-fertility herds Nulliparous heifers Primiparous cows
0.299
0.239 0.282
High-fertility herds Nulliparous heifers Primiparous cows
0.266
-0.273 0.563***
*** P < 0.001 Nutrition
Data
During the analysis of computerized herd feeding schedules and laboratory data, a considerable number of differences were found between the feeding practices of low-fertility herds and high-fertility herds. These differences were related to nutrition during the lactation period as well as to the dry period. Protein
Factor
The percentage of protein in the ration fed during the high stage of lactation and throughout the lactation was significantly higher in low-fertility herds than in high-fertility herds (P c 0.05 and P < 0.01, respectively; Table 4). During
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393
lactation, the ratio net energy (Mcal)/protein (kg in 1 kg dry matter) was significantly higher in high-fertility herds than in low-fertility herds (Table 4). During the dry period, the ratio net energy (Mcal)/protein (kg in 1 kg dry matter) was significantly lower in high-fertility herds than in low-fertility herds. This discrepancy may be explained by the trend to feed high amounts of protein to lactating cows, and reducing protein intake during the dry period. Distiller grains were fed more often to high-fertility herds than to low-fertility herds (Table 4). Distiller grains having a relatively high percentage of undegradable protein may contribute to a proper proportion between degradable and undegradable proteins in the ration. Overfeeding
Factor
There was a clear trend towards feeding higher levels of energy during the second half of the lactation and during the dry period in low-fertility herds than in high-fertility herds. This trend was manifested by feeding higher amounts of dry matter during the second half of the lactation (P c 0.05) in low-fertility herds and by keeping all lactating cows in one feeding group in low-fertility herds - a practice connected with an increased risk of overfeeding toward the end of lactation (Table 4). During the dry period, the average amount of lactating cow mix fed to the dry cows and the percentage of herds being fed increased amounts of this mix (above 3 kg dry matter daily) was significantly higher in low-fertility herds than in high-fertility herds. Similarly, the percentage of herds being fed high levels of energy during the dry period (above 15 Meal net energy) was higher in low-fertility herds than in high-fertility herds (Table 4). The percentage of herds with more than one third of dry cows with body condition scores of 3.5 and above was higher in low-fertility herds than in highfertility herds (P = 0.06). The herds in which at least one factor such as high amount of mix, high level of energy, or high percentage of fat cows existed during the dry period were classified as herds with faulty dry period nutrition. Such a nutritional plane was evident in approximately 60% of low-fertility herds and 23% of high-fertility herds (P = 0.0034; Table 4). The average body score of dry cows in low-fertility herds was significantly higher than in high-fertility herds (P c 0.05; Table 4). Phytoestrogens The roughage samples from 17 low-fertility herds and from 8 high-fertility herds (silage and alfalfa hay), suspected for phytoestrogen activity because of the high incidence of cystic ovaries or of anestrus, were sent to the Kimron Veterinary Institute, Beit Dagan, Israel, for examination. Estrogenic activity of above 50 rig/g was considered to be a positive finding. Eight samples from low-fertility herds were positive while all samples from high-fertility herds were negative (Table 4).
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Theriogenology
Table 4. Differences in nutritional factors between overall conception rates (Model 1)
herds with high and low
Overall conception rate > 45% < 40% Lactation Period Percentage of protein high lactation period
Significance
in 17.14 * 0.14
16.66 +- 0.14
0.0214
Average percentage of protein during lactation
17.11 -c 0.15
16.51 2 0.15
0.0080
Energy/protein
10.07 * 0.11
10.43 -c 0.11
0.0399
ratio
Dry matter in the second half of lactation (kg)
20.3 ? 0.2
19.1
* 0.2
0.0315
Herds with one nutrition group (%)
34.2 r 7.2
12.5
+ 7.2
0.0443
Herds using a selfcutting-cart (%)
18.9 2 8.5
44.4
c 8.5
0.0456
Herds fed distiller grains (%)
3.33 & 5.76
20.00 f 5.76
Herds with phytoestrogens (estrogenic activity > 50 rig/g)) in silage or hay (%)
27.6 + 6.2
f 0.0
0.0089
17.5 2 5.3
13.1 2 7.8 9.5 -+ 7.1 2.5 r 5.3
0.0209 0.0906 0.0604
Percentage of herds with faulty dry period nutrition (a+b+c)
60.5 + 8.4
22.9
0.0034
Energy/protein ratio during the first part of the dry period
13.91 i 0.43
12.53 ~?r0.43
0.0283
Body condition (scale 1 to 5)
2.83 + 0.03
2.72 + 0.03
0.0422
Dry Period Percentage of herds with a) > 3 kg of high lactation mix b) > 15 Meal net energy c) > 30% obese cows
40.2 r 7.8 27.2 -+ 7.1
0.0
0.0452
+ 8.4
score
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395
Self-Cutting-Cart The self-cutting-cart for preparing the mix was used in 13 high-fertility herds and in 6 low-fertility herds (P = 0.0456). The positive effect of using this type of cart is the smooth cut of the silage surface by the self-cutting device, which apparently contributed to better conservation of silage, avoiding it’s dispersion on the floor of the bunker. Nutrition-based
Variance
in Reproductive
Indices, Milk Yield and Body Condition
To evaluate the influence of nutrition on reproduction, milk yield and body condition a linear model with all the nutritional factors to explain the variables was employed (Model 2). In the multiparous cows, the nutritional plane accounted for 67% of the variance in the overall conception rate and 71 to 77% of the variance in days from calving to the first insemination, days open, and days between the first and last insemination (Table 5). The difference in overall conception rate between low-fertility herds and high-fertility herds was reduced from 11 to 1.9% in primiparous cows and from 13.1 to 3.9% in multiparous cows when the effects of nutrition were removed. For the postpartum and post-insemination anestrus, nutritional factors explained 54 to 57% of the variance (Table 5). Furthermore, 65.7% of the variance of the yearly fat-corrected milk production was explained by nutritional factors as well as 50 to 67% of the variance in body condition score during the dry period (Table 5). In the primiparous groups of cows, the variance explained by nutritional factors was similar, but generally lower than that for multiparous cows (Table 6). In multiparous cows, the body condition factor during the dry period explained 4.8% of the variance in the overall conception rate; for days from calving to the first insemination, days open, and days between the first and last insemination the corresponding values were 5, 6.8 and 10.9%, respectively (Table 7). The increase in body condition of multiparous cows was connected with a longer period to conception and a the first and last insemination; the incidence of postpartum anestrus was higher and milk yield was lower with the condition (Table 7).
during the dry period longer period between and post-insemination increase in the body
In primiparous cows, the variance explained by body condition score during the dry period was 1.7% for days from calving to first insemination and 5.6% for days open. For the other indices, the variance was lower than 1% (Table 7). An increasing body condition score in primiparous cows was connected to a higher milk yield and to improved reproductive indices (Table 7).
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Theriogenology
Table 5. Variance explained by nutritional factors (R2) and multiple correlation coefficients (r,) between nutrition and milk yield, reproductive indices, reproductive disorders, and body condition in multiparous cows (Model 2)
Nutritional R2( %)
Milk yield Fat corrected Milk (kg) Fat (%)
milk yield (kg)
Reproductive indices Overall conception rate Days from calving to the first insemination Days from the first to the last insemination Days open Reproductive disorders High incidence of - postpartum anestrus - post-insemination anestrus Body condition in the dry period Body score > 30% obese cows Percentage of cows with body condition score > 3
factors rm
Significance
65.7 67.1 59.2
0.81 0.82 0.77
0.0613 0.0445 0.1997
67.0 71.1
0.82 0.88
0.0132 0.2009
77.5 77.1
0.88 0.88
0.2009 0.1632
57.6 53.9
0.76 0.73
0.1624 0.2753
50.2 51.1
0.71 0.72
0.4513 0.3083
66.6
0.82
0.1078
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397
Table 6. Variance explained by nutritional factors (R2) and multiple correlation coefficients (r,) between nutrition and milk yield, reproductive indices, reproductive disorders, and body condition in primiparous cows (Model 2) Nutritional R2(%) Milk yield Fat corrected Milk (kg) Fat (%)
milk yield (kg)
factors rm
Significance
60.8 61.5 65.5
0.78 0.78 0.81
0.1542 0.1374 0.0647
68.6 57.1
0.83 0.85
0.0080 0.3922
72.0
0.85
0.3922
Reproductive disorders High incidence of - postpartum anestrus - post-insemination anestrus
47.3 52.8
0.69 0.73
0.5319 0.3135
Body condition Body condition
71.1
0.84
0.3586
Reproductive indices Overall conception rate Days from calving to the first insemination Days from the first to the last insemination
Number
in the dry period score
of Risk Factors
The following nutritional factors were significantly different between lowfertility herds and high-fertility herds (Least-Squares Model 1) and were considered to be reproductive risk factors: a 17% or higher level of protein in the lactation period; an energy/protein ratio below 10 : 1 in the lactation period and the allocation of only one nutritional group during the whole lactation; phytoestrogens in silage or hay; and faulty nutritional plane during the dry period. One or more fertility risk factors were found in 18 high-fertility herds and in 29 low-fertility herds. The total number of identifiable risk factors among all highfertility herds and low-fertility herds was 29 and 83, respectively. Among the highfertility herds, there was one herd with three fertility risk factors, while there were 20 low-fertility herds with three and more risk factors.
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Table 7. Variance explained by body condition during the dry period (R2) and correlation coefficients (r) between body condition and milk yield, and reproductive indices, and reproduction disorders in multiparous (M) and primiparous (P) cows (Model 3)
r
R2(%)
Milk yield Fat corrected Milk (kg) Fat (%)
milk (kg)
Reproductive indices Overall conception rate Days from calving to the first insemination Days from the first to the last insemination Days open Reproductive disorders High incidence of - postpartum anestrus - post-insemination anestrus
M
Significance P
M
P
M
P
1.9 2.5 0.1
0.7 0.2 0.7
-0.138 -0.157 0.021
0.082 0.041 0.083
0.3054 0.2424 0.8726
0.6016 0.7955
4.8 5.0
0.9
-0.220 -0.224
0.093
1.7
-0.132
0.1005 0.1589
0.5525 0.4650
10.9
0.3
0.330
-0.053
0.0379
0.7730
6.8
5.6
0.261
-0.237
0.0994
0.1850
0.7 5.4
0.4 0.6
0.084 0.232
-0.124 -0.077
0.5442 0.0879
0.4330 0.6265
0.5991
DISCUSSION The aim of this investigation was to determine which factors predispose Kibbutz dairy herds to high or low fertility using the methods of case-control epidemiological studies. Both, the high- and the low-fertility groups of herds studied had similar, above average of milk yields ranging from 8,000 to 10,000 kg milk per year. Significant differences in the overall conception rates among multiparous and primiparous cows and nulliparous heifers demonstrate that factors predisposing cows to low fertility appear in all parity groups.
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399
The difference between the overall conception rate of multiparous cows between high-fertility herds and low-fertility herds was expected considering that herds were selected according to multiparous conception rate. The multiparous and the primiparous cows in the herds were kept in close proximity under identical environmental and management conditions, and the study animals were fed according to the same nutritional scheme; therefore, the effects of the influencing factors on reproductive indices of both parity groups in low-fertility herds and high-fertility herds would be expected to be similar. Looking at the differences in the overall conception rate between multiparous and primiparous cows it seems that primiparous cows were less sensitive to factors predisposing them to low fertility than were the multiparous cows. Therefore if the factors predisposing to low fertility are moderate, the overali conception rate of primipara may not be markedly impaired. The low correlation coefficients between primiparous and multiparous in low-fertility herds indicate that the negative influence of factors impairing fertility seems to be of major importance in low-fertility herds than in high-fertility herds. The overall conception rate of nulliparous, which were kept apart from the dairy cows and were fed according to a different nutritional scheme should not have been influenced by the selection of herds according to the overall conception rate of the multiparous cows. However, in this study the overall conception rate of nullipara was significantly lower in low-fertility herds than in high-fertility herds. Additionally, the low correlations between the overall conception rate of nullipara and primi-/multipara in high- and low-fertility groups of herds point to increasing fertility problems with the beginning of lactation and adaptation of nutrition to the lactating cows. Similar low correlations between nulliparous heifers and lactating cows were found by Ron et al. (1) in IsraeliHolsteins herds. In view of these findings, it is evident that general herd management and some possible factors not investigated in this study such as genetic effects and viral diseases may have a detrimental influence on the overall conception rate of all parity groups. The longer period from the first to last insemination in low-fertility herds was partially related to a high incidence of post-insemination anestrus, which was five to seven times higher in low-fertility herds than in high-fertility herds. Longer periods from the first to the last insemination together with a high percentage of herds having a high incidence of post-insemination anestrus in low-fertility herds, point to the serious reproductive disturbances found in low-fertility groups of herds. The difference in days open between the low-fertility herds and highfertility herds was small and approached significance only for multiparous cows. However, the parameter of days open was related only to the pregnant cows, and may therefore be strongly biased, especially within herds in which a high percentage of cows that did not conceive was culled. The shortcomings of the days open
400
Theriogenology
index or of the intercalving interval index for determining herds fertility status are emphasized by Bdhm (2), Noordhuizen (3) and Sonderegger (4). The polyfactorial character of the herd infertility syndrome is demonstrated by our data on 17 factors which were significantly different between low-fertility herds and high-fertility herds, and these findings are consistent with data of other researchers (5, 6, 7, 8, 9, 10, 11, 12, 13). Factors occurring more frequently in low-fertility herds were considered to be risk factors for infertility, while those occurring more frequently in high-fertility herds were considered to be fertility promoting factors. With the exception of phytoestrogens, which were found in low-fertility herds only, all the other factors were diagnosed in both fertility groups of herds. The total number of the risk factors was in high-fertility herds significantly lower than in low-fertility herds. Thus, it appears that risk factors have a cumulative influence on reproductive performance. Nutritional parameters had the highest influential effect on differences in reproductive performance between herds with similar production levels kept under similar environmental conditions. High protein levels were found to influence fertility adversely in high milk producing cows. This negative effect of high protein levels on reproductive performance is consistent with the findings of Brochart et al. (14), Canfield et al. (l-5), Frances and Mayer (16), Jordan and Swanson (17), Kaim et al. (18), Kaufmann (19) and Sonderegger (4), but differs from those of Carroll et al. (20) and Howard et al. (21). The energy/protein ratio fed during lactation and the dry period was connected with reproductive efficiency. Detrimental effects of either a low or high energy/protein ratio are also supported by Garibay Vila (22), Hafner and Schulz (23) and Busch et al. (24). Feeding high levels of energy at the end of lactation and dry period increased the average body score of dry cows significantly in low-fertility herds compared with high-fertility herds. Feeding of the same ration to all cows during the entire lactation period appeared to be connected with the risk of overconditioning toward the end of the lactation and during the dry period (25, 26, 27). The amount of dry matter fed during the second half of the lactation was higher in low-fertility herds than in high-fertility herds. A clear trend to overconsumption during the dry period and towards the end of lactation was observed in the low-fertility herds. Nevertheless, most of the dry cows were not obese, and a clear trend towards obesity was found only in 20% of low-fertility herds. Dry period overconditioning of cows can result in significantly high hepatic lipidosis, which can cause reproductive problems (27, 28, 29, 30). Although high levels of
Theriogenology
401
prepartum feeding may not result in overconditioning during the dry period, it does increase postpartum reproductive problems and elevates hepatic lipidosis severely (31, 32, 33, 34). In the herds surveyed in our study, the incidence of postpartum metabolic problems was low. Since biochemical examinations of the blood and liver were not included in our study, we can only assume that the low reproductive performance of low-fertility herds was influenced by hepatic lipidosis connected with high postpartum milk yield and with the high Ievel of nutrition during the dry period. An increase in body condition scores during the dry period among multiparous cows was connected with negative reproductive indices (with the exception of days from calving to first insemination). This was particularly evident for the wasted days index (days from the first to the last effective or ineffective insemination). This finding indicates that risk factors acting during the prepartum period influence reproductive performance for many months after calving (35, 36, 37, 38). Increased body condition in primiparous cows, as opposed to that in multiparous cows, contributed to more accurate reproductive indices. Early primiparous cows may have better body condition and fertility indices than primiparous cows that mature later; however, it could not be established if the early maturing cows become overconditioned in the dry period and thus may be exposed to more fertility problems in subsequent lactations in comparison with late maturing cows. Although differences in the absolute values of factors influencing fertility levels in high-fertility herds and low-fertility herds (see Table 4) were generally small, those factors were significantly correlated with herd fertility levels, thus demonstrating the high correlation between nutritional/metabolic factors and reproductive processes in high milk producing cows (39, 40). The negative influence of phytoestrogenic activity on reproductive performance that was found in this study is consistent with the data of others (41, 42, 43, 44). Therefore, examining suspected problem herds for the presence of phytoestrogens is recommended. Analysis of the data in this study strongly emphasizes the multifaceted character of influences on reproductive processes. In the course of this investigation, 17 different risk factors were identified, most of which were nutritional; approximately two-thirds of the differences existing between the overall conception rates of high- and low-fertility herds were explained by these nutritional factors. The longlasting effects of the fertility risk factors acting during the dry period on the postpartum reproductive performance, like that of overconditioning and the feeding of unbalanced rations, reflects the limited capacity of high milk producing dairy cows to return to the reproductive function disturbed by the postpartum period.
402
Theriogenology
This very fragile balance between nutrition and reproduction, apparently mediated through the linkage between metabolic and hormonal factors, is demonstrated by the findings that even relatively small differences in the level of protein, energy/protein ratio, body scoring during the dry period were connected with a marked decrease in reproduction indices. The connection between the number of fertility risk factors and the fertility rate within a herd demonstrates that herd fertility problems can be remedied by removing the risk factors. Extensive epidemiological studies combined with properly controlled experiments are needed to determine the thresholds of the nutritional factors contributing to both optimal milk yield and to high fertility in high milk producing dairy cows.
REFERENCES 1. Ron, M., Bar-Anan, R. and Wiggans, G.R. Factors affecting of Israeli Holstein cattle. J. Dairy Sci. 67: 854-860 (1984).
conception
rate
2.
Bohm, M. Untersuchungen zur Entwicklung von Betriebskennzahlen der Fruchtbarkeitsleistung in Besamungsbetrieben mit Milchleistungspriifung. Dissertation Med. Vet. University of Munich, 1989.
3.
Noordhuizen, J.P.T.M. Veterinary Herd Health and Production Dairy Farms. Ph. D. Dissertation University of Utrecht, 1984.
4.
Sonderegger, J. Die Fruchtbarkeit des Rindes einigen Ernahrungsfaktoren. Dissertation Med. 1976.
5.
Bostedt, H. Beitrag zur Problematik der Uberwachung von Milchrinderbestanden mit verminderter Fertilitat. Prakt. Tierarzt 61, Colleg. Vet. x: 39-44 (1980).
6.
Call, E.P. and Stevenson, J.S. Current J. Dairy Sci. &3: 2799-2805 (1985).
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Coleman, D.A., Thayne, W.V. and Dailey, R.A. Factors affecting reproductive performance of dairy cows. J. Dairy Sci. 68: 1793-1803 (1985).
8.
Frances, G., Mayer, E. and Davidson, M. Nutritional influence on first insemination conception and the repeat breeder syndrome. Proc. XIth Intern. Congress on Diseases of Cattle (Tel Aviv), pp. 833-839 (1980).
und Vet.
Control
on
ihre Beziehungen zu University of Zurich,
challenges in reproductive
management.
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9.
403
Mayer, E., Frances, G. and Davidson, M. Nutritional influence on fertility in Israeli dairy herds with an average 305day production per cow of 8000 kg of fat-corrected milk. Theriogenology 9: 393-400 (1978).
10. O’Connor, M.L., Baldwin, R.S. Adams, R.S. and Hutchinson L.J. An integrated approach to improving reproductive performance. J. Dairy Sci. @: 28062816 (1985). 11. Oltenacu, P.A., Britt, J.H., Braun, R.K. and Mellenberger, R.W. Effect of health status on culling and reproductive performance of Holstein cows. J. Dairy Sci. 67: 1783-1792 (1984). 12. Pelissier, C.L. Field breeding 55: 385-391 (1972).
problems
and their consequences.
13. Schefels, W. and Stolla, R. Zur Diagnose und Therapie sterilitat des Rindes. Tierarztl. Umsch. 40: 458-466 (1985).
J. Dairy Sci.
bei der Herden-
14. Brochart, M., Gaulliard, D. and Girou, R. Energie und Eiweil3niveau Flushing nach der Brunst und Fruchtbarkeit bei Milchkiihen. VII. Int. Kongrel3 fur tierische Fortpflanzung und Haustierbesamung, Miinchen, Proc. III, pp. 1737-1741 (1972). 15. Canfield, R.W., Sniffen, C.J. and Butler, W.R. Effects of high dietary crude protein on postpartum reproduction. Ann. Meet. Amer. Dairy Sci. Assoc. J. Dairy Sci. 21 (Supple.): 171 abstr. (1988). 16. Frances, G. and Mayer, E. Observations on some environmental factors connected with fertility in heat stressed cows. Theriogenology 19: 625-634 (1983). 17. Jordan, E.R. and Swanson, L.V. Effects of crude protein on reproductive efficiency, serum total protein and albumin in the high-producing dairy cow. J. Dairy Sci. 62: 58-63 (1979). 18. Kaim, M., Folman, Y., Neumark, H. and Kaufmann, W. The effect of protein intake and lactation number on postpartum body weight loss and reproductive performance of dairy cows. Anim. Prod. 3: 229-235 (1983). 19. Kaufmann, W. Zur Bedeutung der Energieversorgung hochleistender Milchkiihe fur den Milcheiweil3gehalt und die Fruchtbarkeit. Kieler Milchwirtschaftliche Forschungsberichte 28: 347-357 (1976).
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y
20. Caroll,
D.J., Barton, B.A., Anderson, G.W. and Smith, R.D. Influence of protein intake and feeding strategy on reproductive performance of dairy cows. J. Dairy Sci. a: 3470-3481 (1988).
21. Howard, H.J., Aalseth, E.P., Adams, G.D., Bush, L.J., McNew, R.W. and Dawson, L.J. Influence of dietary protein on reproductive performance of dairy cows. J. Dairy Sci. 70: 1563-1.571 (1987). 22. Garibay Vila, M.E. Einflul3 der Energie- und Eiweil3versorgung in der Hochtriichtigkeit auf Stoffwechsel- und Fruchtbarkeitssch$den bei Milchrindern. Dissertation Med. Vet. University of Hanover, 1978. 23. Hafner, L. and Schulz, J. Die Fruchtbarkeit von Milchkiihen bei unterschiedlithen Varianten der Leistungsfiitterung. Mh. Vet. Med. 44: 826-830 (1989). 24. Busch, W., Filrstenberg, L. and Menzke, V. Stabilisierung der Fruchtbarkeit in Rinderherden durch Einhaltung des optimalen Protein/Energieverhaltnisses. Tierzucht 2: 462-464 (1985). 25. Higgins, R.J. and Anderson, W.C. Fat cow syndrome Vet. Rec. 113: 461-463 (1983).
in British dairy herds.
26. Markusfeld, 0. Factors responsible Vet. Rec. 114: 539-542 (1984).
metritis in dairy cattle.
27. Morrow,
D.A. Fat cow syndrome.
for post parturient
J. Dairy Sci. 3:
1625-1629 (1976).
28. Fronk, T.J., Schultz, L.H. and Hardie, A.R. Effect of dry period overconditioning on subsequent metabolic disorders and performance of dairy cows. J. Dairy Sci. g: 527-531 (1980). 29. Reid, I.M., Rowlands, G.J., Dew, A.M., Collins, R.A., Roberts, C.J. and Manston, R. The relationship between postparturient fatty liver and blood composition in dairy cows. J. Agric. Sci. 101: 473-480 (1983). 30. Sttiber, M. and Dirksen, G. Das Lipomobilisationssyndrom (Verfettungssyndrom) der Milchkuh. Prakt. Tierarzt 63 Colleg. Vet. XII: 79-88 (1982). 31. Flipot, P.M., Roy, G.L. and Dufour, J.J. Effect of peripartum energy concentrations on production and performance of Holstein cows. J. Dairy Sci. a: 1840-1850 (1988). 32. Gerloff, B.J., Herdt, T.H. and Emery, R.S. Relationship of hepatic lipidosis to health and performance in dairy cattle. J. Amer. Vet. Med. Assoc. 188: 845-850 (1986).
405
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33. Keys, J.E., Pearson,
R.E. and Miller, R.H. Effect of ratio of corn silage to grass legume silage with high concentrate during dry period on milk production and health of dairy cows. J. Dairy Sci. 67: 307-312 (1984).
34. Reid,
I.M., Roberts, C.J., Treacher, R.J. and Williams, L.A. Effect of body condition at calving on tissue mobilization, development of fatty liver and blood chemistry of dairy cows. Anim. Prod. 43: 7-15 (1986).
35. Frances, G. Possible effect of different nutritional planes on the incidence reproductive disorders in Israeli dairy herds. Refu. Vet. 3-l: 27-32 (1974). 36. Frances, G. Beobachtungen zum Auftreten von Fortpflanzungsstiirungen Milchviehherden in Israel. Dtsch. tierarztl. Wschr. a: 135-138 (1974).
of
bei
37. Frances, G. and Mayer, E. Computerized analysis of the incidence of bovine reproductive disorders. A tool for managing herd fertility problems. Proc. Sot. Vet. Epidemiol. and Prev. Med., Reading, pp. 144-154 (1985). 38. Markusfeld, 0. The evaluation of a routine treatment with la-hydroxyvitamine D, for the prevention of bovine parturient paresis. Prev. Vet. Med. 1: 1-9 (1989). 39. Farries, E. Beziehungen zwischen Haltung Tierarztl. Praxis 11: 169-185 (1983).
und Fruchtbarkeit
beim Milchrind.
40. Frances, G., Shamir, I. and Mayer, E. A survey of summer fertility in family sized Israeli dairy herds during a four-year period. XIVth World Congress on Diseases of Cattle (Dublin), pp. 915-923 (1986). 41. Adler, J.H. and Trainin, D. The apparent effect of alfalfa on the reproductive performance of dairy cattle. Proc. 4th Int. Congr. Anim. Repr. 451 abstr. (1961). 42. Jorgensen, N.A. and Freymiller, J. Dairy Sci. 55: SO-82 (1972).
D.D. Estrogenic
activity of fermented
alfalfa.
43. Kalac, P. and Woolford, M.K. A review of some aspects of possible associations between the feeding of silage and animal health. Brit. Vet. J. 138: 305320 (1982). 44. Lotan, E. and Adler, J.H. Early effects of excessive alfalfa feeding on bovine fertility. Refu. Vet. 22: 110-112 (1966).
EPIDEMIOLOGICAL STUDY ON FACTORS INFLUENCING FERTILITY INDICES IN ISRAELI DAIRY HERDS G. Frances,’
0. Distl:
H. Krau131ich2 and E. Mayer?
‘Hahaklait Clinical Veterinary Services, P.O.B. 9610 Haifa, Israel ‘Institut fur Tierzucht und Tierhygiene der Universitat Miinchen VeterinarstraBe 13, 8000 Miinchen 22, FRG 31nstitute for Veterinary Clinical and EpidemioIogical Research P.O.B. 9610, Haifa, Israel Received
for publication: April 3, 1991 Accepted: JUZ~ 12, 2992 ABSTRACT
The objective of this study was to determine feeding factors connected with differences in the fertility of Israeli Kibbutz dairy herds. In an epidemiological case-control survey, data from 30, low-fertility Kibbutz dairy herds having a mean overall conception rate of 35% in multiparous cows were compared with the data from 30, high-fertility Kibbutz dairy herds having a mean overall conception rate of 48% in multiparous cows. Nutritional factors accounted for 67% of the differences between low-fertility and high-fertility herds in the overall conception rate of multiparous cows, while only 4.8% could be related to the body condition during the dry period. Among the factors which occurred more frequently in the low-fertility than in the high-fertility herds were 1) a higher average protein density and lower energy/protein ratio was fed during lactation and 2) a single feeding group was maintained for all lactating cows. 3) There were phytoestrogens in the silage or alfalfa hay, fed during lactation. 4) Faulty dry period was instituted, which was defined as the presence of at least one of the following three practices: a) the daily feed was above 3 kg of high lactation mix; b) more than 15 Meal of net energy per day was given during the first part of the dry period; c) more than 30% of the cows were obese during the dry period. Three or more risk factors were found in one high-fertility herd and in 20 low-fertility herds. This finding emphasizes the importance of identifying and removing risk factors as a possible means for improving the reproductive performance of herds. Key words: epidemiological
study, fertility, dairy cattle, nutrition
Acknowledgments This study was supported by a grant from the Research Fund of the Israeli Milk Marketing Board and the Israeli Cattle Breeders’ Association, Tel Aviv. The authors thank D. Avieli, M. Ben Meir, Dr. 0. Nir and D. Peri for their help as well as the veterinarians and staffs of the herds used in this study.
Copyright 0 1992 Butterworth-Heinemann
386
Theriogenology
INTRODUCTION The aim of our investigation was to determine the factors which influence herd fertility levels in Israeli Kibbutz dairy herds. These were commercial dairy herds with an average of 300 cows yielding an average milk yield of 8,000 to 11,000 kg per year. In spite of apparently similar management systems, an uniform genetic background and a similar pattern of veterinary and insemination services, the differences in fertility indices between the herds were considerable. To identify the factors related to differences in reproductive performance we undertook a wide-scale epidemiological study of low- and high-fertility herds. MATERIALS
AND METHODS
Sixty Kibbutz herds with 18,900 dairy cows were included in this study. The herds were selected according to the data on overall conception rate, which was derived from herd book records. The overall conception rate was calculated as the percentage of the number of multiparous cows with conceptions divided by the number of inseminations performed in all multiparous cows, regardless of whether or not pregnancy was established. Thirty herds, having an overall conception rate of more than 45% among cows from the second and subsequent lactations during the months of November to June, were classified as high-fertility herds. The remaining 30 herds with an overall conception rate of less than 40% the same period were classified as low-fertility herds. Selection on the basis of overall conception rates in the autumn-spring months was intended to eliminate the influence of the hot summer period. The number of cows in the surveyed herds varied from 235 to 460 head; the average yearly milk production of the cows from the second lactation and onwards varied from 8,100 to 11,000 kg. The herds were located all over the country with the exception of the Jordan Valley and the Southern Negev (desert) regions. Each herd was visited one or two times from July 1987 to January 1989. The following reproductive indices of primiparous and multiparous cows were recorded: 1) days from calving to the first insemination; 2) days from the first to the last insemination (wasted days); 3) days from calving to conception (days open); 4) average yearly milk yield (based on herd records); 5) incidence of reproductive disorders based on data derived from either local veterinary records or from records of the Israeli Herd Book and 6) herd incidence of postpartum anestrus if occurrence was above 25%. The postpartum anestrus was defined as no observable estrous behaviour prior to 60 days postpartum and no other reproductive disorder noted until 60 days postpartum. The percentage of herds with a
Theriogenology
387
high incidence of post-insemination anestrus was calculated using the incidence of cows being diagnosed not pregnant by palpation per rectum at 40 to 50 days after insemination. The cutoff point for herds classified as high incidence post-insemination anestrus was 22%. Detailed data on the allocation of each herd to nutritional groups as well as the food components and the exact feeding schemes of these groups were recorded. The nutritional values of the concentrate foods were calculated from the producer’s analysis or from national tables; roughage values were determined from laboratory data based on the examination of the samples sent by herd managers or by the investigators. The following feed factors were recorded: 1) the dry matter content of ration fed to high and low milk producing cows and average dry matter intake during the entire lactation; 2) parallel data were recorded on net energy per kilogram of dry matter; 3) the percentage of protein and 4) the percentage of roughage. Data on the feeding regimens during the dry period, which generally lasted 8 weeks, were recorded separately for the first 5 to 6 weeks of the dry period and for the final 2 to 3 weeks. The following data were included: 1) total dry matter intake; 2) net energy intake; 3) protein intake and 4) the mix, silage and hay intake during each of those periods. Additional factors connected with nutrition were the feeding of distiller grains during lactation, the feeding of whey during the lactation, the use of self loading cart with attached rotating knife for cutting silage (self-cutting-cart) for the preparation and distribution of mix, the examination of roughage for fungi contamination and for phytoestrogens and the examination of silage bunkers. Most samples of herd silage and occasional hay samples were sent mycotic examination. In the 25 herds in which hyperestrogenic activity was ted, forage samples were sent out for examination of phytoestrogen levels The mycotic and phytoestrogen examinations were performed at the Veterinary Institute, Beit Dagan, Israel.
out for suspecas well. Kimron
Body condition was scored on a scale of 1 to 5 and was assessed for dry cows and nulliparous heifers in the last 2 months of gestation. Additional data were recorded on instances of observed estrous and the type of housing in which the animals were maintained.
388
Theriogenology
Statistical
Methods
Fertility indices, nutrition and management factors, based on herd averages, were tested on significant differences between low-fertility herds and high-fertility herds using the following linear least-square model (Model 1): yijW
Yijkl Ei,bj Mi Fj HC, eijW
=
: : : : : : :
/J + bt Mi + bj Fj + HC, + eyu; dependent variable (fertility index or nutritional factor of the ijkl-th herd) model-dependent constant individual linear regression coefficients for Mi and Fj, respectively yearly average milk yield of herdij, yearly average percentage of fat of herd,ju herd class low-fertility herds or high-fertility herds remaining factors
Variance explained by nutritional linear least-square model (Model 2): Yij yij
b”. ii
eij
factors was quantified
by the following
= p + Zb& + eij; : dependent variable of the ij-th herd : model-dependent constant : individual linear regression coefficients for effects included in & : the following nutritional factors were regarded simultaneously as individual effects in the model: intake of dry matter, net energy, protein, and roughage during lactation in all cows and in high producing cows; feeding regimen in the dry period (intake of dry matter, net energy, protein, mix, silage and hay); feeding of distiller grains during lactation; feeding of whey during lactation; division into feeding groups; use of a self-cuttingcart for preparation and distribution of feed mix, phytoestrogenic activity of roughage/silage; and examination results of silage bunkers (i = 1 to 20) : remaining factors
A similar model was applied to analyze the effect of body condition during the dry period on milk production and on reproductive indices and disorders. In this model only the effect of body condition score during the dry period was regarded as an independent variable (Model 3): Yij yij
bi BC, eii
= : : :
p + bi BC, + eij; milk production or reproductive index or disorder of the ij-th herd linear regression coefficient average body condition score of dry cows or nulliparous heifers in the last 2 months of gestation of the ij-th herd : remaining factors
Theriogenology
Variance the goodness R2 = R (X) = b x Y’Y
: : :
explained by the different models (R’) was used as a measure of fit by the model applied and was computed as follows:
of
R (X) / Y’Y = b’X’Xb / Y’Y, b’X’Xb: reduction in sum of squares corrected for mean by the model applied solution vector model-dependent design matrix total variance of the dependent variable Y corrected for the mean
The multiple correlation coefficient (r,) was estimated as the product moment correlation between the observed Y and the predicted Y and was calculated as the square root of R’.
RESULTS Milk Yield Fat corrected milk values were similar in both groups of herds, but the lowfertility herds had significantly higher milk production averages and significantly lower fat percentage averages in comparison with the high-fertility herds (Table 1). Overall Conception
Rate
Nulliparous heifers had the highest overall conception rate, while multiparous cows had the lowest. The differences in the overall conception rates between parity groups are a feature of Israeli dairy herds. The overall conception rate of nulliparous, primiparous and multiparous in high-fertility herds was significantly higher than the overall conception rate of the corresponding parity group in the low-fertility herds (Table 2). It appears that the factors impairing fertility levels affect all parity groups in low-fertility herds (Table 2). In high-fertility herds the correlation between the overall conception rate of primiparous and multiparous cows was significantly different from zero (r = 0.563); the corresponding coefficient of correlation in low-fertility herds was much lower (r = 0.282) (Table 3). The correlations between the overall conception rate of nulliparous cows and of the cows were in the range from -0.273 to 0.299 (Table 3).
390
Table
Theriogenology
1. Average yearly milk yield in 30 herds with high and 30 herds with low overall conception rate Overall conception < 40%
rate > 45%
Significance
Milk yield (kg) Primiparous Multiparous
cows cows
9267 ” 112 10091 * 137
cows cows
3.08 + 0.04 3.06 + 0.04
8918 9773
2 112 + 137
0.0316 0.1066
Fat (%) Primiparous Multiparous Fat corrected Primiparous Multiparous
3.22 k 0.04 3.19 2 0.04
0.0057 0.0237
milk yield (kg) cows cows
7985 8667
+ 110 + 135
7882 8580
2 110 r 135
0.5145 0.6484
Days from Calving to the First Insemination The number of days to the first insemination was similar in both herds of primiparous animals. Multiparous cows in the low-fertility herds had a significantly (P = 0.006) shorter period to the first insemination than cows in high-fertility herds. It appears that this difference was strongly influenced by the efforts of the managers of low-fertility herds in order to compensate for the delay in conception by early insemination (Table 2). Wasted Days (Days Between
the First and Last Insemination)
There were significantly fewer wasted days (P < 0.001) in high-fertility herds than in low-fertility herds, with 18.6 days for primiparous cows and 24.6 days for multiparous cows (Table 2). A high incidence of negative pregnancy diagnoses in low-fertility herds contributed to the difference (Table 2). Days Open (Days from Calving to Conception) Fewer days to conception were recorded fertility herds with 5.5 days for primiparous cows (Table 2).
for high-fertility herds than for lowcows and 9.6 days for multiparous
391
Theriogenology
Table 2. Reproductive indices in dairy herds with high (n=30) overall conception rate (Model 1)
Overall conception
rate >45%
< 40%
and low (n=30)
Sienificance
Overall conception rate (%) Nulliparous Primiparous Multiparous
heifers cows cows
55.4 k 9.2 42.0 -+ 1.3 35.1 + 0.6
63.8 + 7.1 52.3 + 1.3 48.1 + 0.6
0.0001 0.0001 0.0001
Days from calving to the first insemination Primiparous Multiparous
cows cows
84.3 -+ 2.1 73.9 ?I 1.2
85.2 + 1.9 80.4 +- 1.1
0.7783 0.0006
cows cows
51.7 * 3.1 61.7 + 2.9
32.3 + 2.7 37.1 + 2.6
0.0001 0.0001
cows cows
125.5 2 3.3 120.3 k 3.6
120.0 2 3.0 110.7 f 3.3
0.2539 0.0708
Days from the first to the last insemination Primiparous Multiparous Days open Primiparous Multiparous
Number of daily scheduled observations of estrus
1.94 k 0.15
2.16 + 0.15
0.2969
High incidence of postpartum anestrus (% of herds) Primiparous Multiparous
cows cows
30.6 -+ 8.0 28.6 + 8.4
11.4 f 20.0 +
7.7 8.1
0.1069 0.4776
5.8 r 10.3 +
7.1 7.6
0.0022 0.0009
High incidence of postinsemination anestrus (% of herds) Primiparous Multiparous
cows cows
40.2 ;t 49.7 r
7.3 7.8
Theriogenology
392 Percentage
of Herds with High Incidence
Postpartum
Anestrus
The difference in the percentage of the herds with a high incidence (above 25%) postpartum anestrus between the two groups of herds was not significant (Table 2); however, the percentage of herds with a high incidence of post-insemination anestrus was higher in low-fertility than in high-fertility herds (Table 2). Percentage
of Herds with High Incidence
Post-Insemination
anestrus
The percentage of primiparous herds with a high incidence (above 22%) of post-insemination anestrus (negative per rectum pregnancy examination) in lowfertility herds and high-fertility herds was 40.2 and 5.8%, respectively (P < 0.01). In multiparous herds the corresponding values were 49.7 and 10.3%, respectively (P < 0.001; Table 2). Thus it appears that the occurrence of a high incidence of post-insemination anestrus is one of the primary factors influencing a low overall conception rate in a herd. Table 3. Correlations primiparous
between the overall conception rate of nulliparous heifers, and multiparous cows in herds with high and low fertility
Primiparous
cows
Multiparous
cows
Low-fertility herds Nulliparous heifers Primiparous cows
0.299
0.239 0.282
High-fertility herds Nulliparous heifers Primiparous cows
0.266
-0.273 0.563***
*** P < 0.001 Nutrition
Data
During the analysis of computerized herd feeding schedules and laboratory data, a considerable number of differences were found between the feeding practices of low-fertility herds and high-fertility herds. These differences were related to nutrition during the lactation period as well as to the dry period. Protein
Factor
The percentage of protein in the ration fed during the high stage of lactation and throughout the lactation was significantly higher in low-fertility herds than in high-fertility herds (P c 0.05 and P < 0.01, respectively; Table 4). During
Theriogenology
393
lactation, the ratio net energy (Mcal)/protein (kg in 1 kg dry matter) was significantly higher in high-fertility herds than in low-fertility herds (Table 4). During the dry period, the ratio net energy (Mcal)/protein (kg in 1 kg dry matter) was significantly lower in high-fertility herds than in low-fertility herds. This discrepancy may be explained by the trend to feed high amounts of protein to lactating cows, and reducing protein intake during the dry period. Distiller grains were fed more often to high-fertility herds than to low-fertility herds (Table 4). Distiller grains having a relatively high percentage of undegradable protein may contribute to a proper proportion between degradable and undegradable proteins in the ration. Overfeeding
Factor
There was a clear trend towards feeding higher levels of energy during the second half of the lactation and during the dry period in low-fertility herds than in high-fertility herds. This trend was manifested by feeding higher amounts of dry matter during the second half of the lactation (P c 0.05) in low-fertility herds and by keeping all lactating cows in one feeding group in low-fertility herds - a practice connected with an increased risk of overfeeding toward the end of lactation (Table 4). During the dry period, the average amount of lactating cow mix fed to the dry cows and the percentage of herds being fed increased amounts of this mix (above 3 kg dry matter daily) was significantly higher in low-fertility herds than in high-fertility herds. Similarly, the percentage of herds being fed high levels of energy during the dry period (above 15 Meal net energy) was higher in low-fertility herds than in high-fertility herds (Table 4). The percentage of herds with more than one third of dry cows with body condition scores of 3.5 and above was higher in low-fertility herds than in highfertility herds (P = 0.06). The herds in which at least one factor such as high amount of mix, high level of energy, or high percentage of fat cows existed during the dry period were classified as herds with faulty dry period nutrition. Such a nutritional plane was evident in approximately 60% of low-fertility herds and 23% of high-fertility herds (P = 0.0034; Table 4). The average body score of dry cows in low-fertility herds was significantly higher than in high-fertility herds (P c 0.05; Table 4). Phytoestrogens The roughage samples from 17 low-fertility herds and from 8 high-fertility herds (silage and alfalfa hay), suspected for phytoestrogen activity because of the high incidence of cystic ovaries or of anestrus, were sent to the Kimron Veterinary Institute, Beit Dagan, Israel, for examination. Estrogenic activity of above 50 rig/g was considered to be a positive finding. Eight samples from low-fertility herds were positive while all samples from high-fertility herds were negative (Table 4).
394
Theriogenology
Table 4. Differences in nutritional factors between overall conception rates (Model 1)
herds with high and low
Overall conception rate > 45% < 40% Lactation Period Percentage of protein high lactation period
Significance
in 17.14 * 0.14
16.66 +- 0.14
0.0214
Average percentage of protein during lactation
17.11 -c 0.15
16.51 2 0.15
0.0080
Energy/protein
10.07 * 0.11
10.43 -c 0.11
0.0399
ratio
Dry matter in the second half of lactation (kg)
20.3 ? 0.2
19.1
* 0.2
0.0315
Herds with one nutrition group (%)
34.2 r 7.2
12.5
+ 7.2
0.0443
Herds using a selfcutting-cart (%)
18.9 2 8.5
44.4
c 8.5
0.0456
Herds fed distiller grains (%)
3.33 & 5.76
20.00 f 5.76
Herds with phytoestrogens (estrogenic activity > 50 rig/g)) in silage or hay (%)
27.6 + 6.2
f 0.0
0.0089
17.5 2 5.3
13.1 2 7.8 9.5 -+ 7.1 2.5 r 5.3
0.0209 0.0906 0.0604
Percentage of herds with faulty dry period nutrition (a+b+c)
60.5 + 8.4
22.9
0.0034
Energy/protein ratio during the first part of the dry period
13.91 i 0.43
12.53 ~?r0.43
0.0283
Body condition (scale 1 to 5)
2.83 + 0.03
2.72 + 0.03
0.0422
Dry Period Percentage of herds with a) > 3 kg of high lactation mix b) > 15 Meal net energy c) > 30% obese cows
40.2 r 7.8 27.2 -+ 7.1
0.0
0.0452
+ 8.4
score
Theriogenology
395
Self-Cutting-Cart The self-cutting-cart for preparing the mix was used in 13 high-fertility herds and in 6 low-fertility herds (P = 0.0456). The positive effect of using this type of cart is the smooth cut of the silage surface by the self-cutting device, which apparently contributed to better conservation of silage, avoiding it’s dispersion on the floor of the bunker. Nutrition-based
Variance
in Reproductive
Indices, Milk Yield and Body Condition
To evaluate the influence of nutrition on reproduction, milk yield and body condition a linear model with all the nutritional factors to explain the variables was employed (Model 2). In the multiparous cows, the nutritional plane accounted for 67% of the variance in the overall conception rate and 71 to 77% of the variance in days from calving to the first insemination, days open, and days between the first and last insemination (Table 5). The difference in overall conception rate between low-fertility herds and high-fertility herds was reduced from 11 to 1.9% in primiparous cows and from 13.1 to 3.9% in multiparous cows when the effects of nutrition were removed. For the postpartum and post-insemination anestrus, nutritional factors explained 54 to 57% of the variance (Table 5). Furthermore, 65.7% of the variance of the yearly fat-corrected milk production was explained by nutritional factors as well as 50 to 67% of the variance in body condition score during the dry period (Table 5). In the primiparous groups of cows, the variance explained by nutritional factors was similar, but generally lower than that for multiparous cows (Table 6). In multiparous cows, the body condition factor during the dry period explained 4.8% of the variance in the overall conception rate; for days from calving to the first insemination, days open, and days between the first and last insemination the corresponding values were 5, 6.8 and 10.9%, respectively (Table 7). The increase in body condition of multiparous cows was connected with a longer period to conception and a the first and last insemination; the incidence of postpartum anestrus was higher and milk yield was lower with the condition (Table 7).
during the dry period longer period between and post-insemination increase in the body
In primiparous cows, the variance explained by body condition score during the dry period was 1.7% for days from calving to first insemination and 5.6% for days open. For the other indices, the variance was lower than 1% (Table 7). An increasing body condition score in primiparous cows was connected to a higher milk yield and to improved reproductive indices (Table 7).
396
Theriogenology
Table 5. Variance explained by nutritional factors (R2) and multiple correlation coefficients (r,) between nutrition and milk yield, reproductive indices, reproductive disorders, and body condition in multiparous cows (Model 2)
Nutritional R2( %)
Milk yield Fat corrected Milk (kg) Fat (%)
milk yield (kg)
Reproductive indices Overall conception rate Days from calving to the first insemination Days from the first to the last insemination Days open Reproductive disorders High incidence of - postpartum anestrus - post-insemination anestrus Body condition in the dry period Body score > 30% obese cows Percentage of cows with body condition score > 3
factors rm
Significance
65.7 67.1 59.2
0.81 0.82 0.77
0.0613 0.0445 0.1997
67.0 71.1
0.82 0.88
0.0132 0.2009
77.5 77.1
0.88 0.88
0.2009 0.1632
57.6 53.9
0.76 0.73
0.1624 0.2753
50.2 51.1
0.71 0.72
0.4513 0.3083
66.6
0.82
0.1078
Theriogenology
397
Table 6. Variance explained by nutritional factors (R2) and multiple correlation coefficients (r,) between nutrition and milk yield, reproductive indices, reproductive disorders, and body condition in primiparous cows (Model 2) Nutritional R2(%) Milk yield Fat corrected Milk (kg) Fat (%)
milk yield (kg)
factors rm
Significance
60.8 61.5 65.5
0.78 0.78 0.81
0.1542 0.1374 0.0647
68.6 57.1
0.83 0.85
0.0080 0.3922
72.0
0.85
0.3922
Reproductive disorders High incidence of - postpartum anestrus - post-insemination anestrus
47.3 52.8
0.69 0.73
0.5319 0.3135
Body condition Body condition
71.1
0.84
0.3586
Reproductive indices Overall conception rate Days from calving to the first insemination Days from the first to the last insemination
Number
in the dry period score
of Risk Factors
The following nutritional factors were significantly different between lowfertility herds and high-fertility herds (Least-Squares Model 1) and were considered to be reproductive risk factors: a 17% or higher level of protein in the lactation period; an energy/protein ratio below 10 : 1 in the lactation period and the allocation of only one nutritional group during the whole lactation; phytoestrogens in silage or hay; and faulty nutritional plane during the dry period. One or more fertility risk factors were found in 18 high-fertility herds and in 29 low-fertility herds. The total number of identifiable risk factors among all highfertility herds and low-fertility herds was 29 and 83, respectively. Among the highfertility herds, there was one herd with three fertility risk factors, while there were 20 low-fertility herds with three and more risk factors.
Theriogenology
398
Table 7. Variance explained by body condition during the dry period (R2) and correlation coefficients (r) between body condition and milk yield, and reproductive indices, and reproduction disorders in multiparous (M) and primiparous (P) cows (Model 3)
r
R2(%)
Milk yield Fat corrected Milk (kg) Fat (%)
milk (kg)
Reproductive indices Overall conception rate Days from calving to the first insemination Days from the first to the last insemination Days open Reproductive disorders High incidence of - postpartum anestrus - post-insemination anestrus
M
Significance P
M
P
M
P
1.9 2.5 0.1
0.7 0.2 0.7
-0.138 -0.157 0.021
0.082 0.041 0.083
0.3054 0.2424 0.8726
0.6016 0.7955
4.8 5.0
0.9
-0.220 -0.224
0.093
1.7
-0.132
0.1005 0.1589
0.5525 0.4650
10.9
0.3
0.330
-0.053
0.0379
0.7730
6.8
5.6
0.261
-0.237
0.0994
0.1850
0.7 5.4
0.4 0.6
0.084 0.232
-0.124 -0.077
0.5442 0.0879
0.4330 0.6265
0.5991
DISCUSSION The aim of this investigation was to determine which factors predispose Kibbutz dairy herds to high or low fertility using the methods of case-control epidemiological studies. Both, the high- and the low-fertility groups of herds studied had similar, above average of milk yields ranging from 8,000 to 10,000 kg milk per year. Significant differences in the overall conception rates among multiparous and primiparous cows and nulliparous heifers demonstrate that factors predisposing cows to low fertility appear in all parity groups.
Theriogenology
399
The difference between the overall conception rate of multiparous cows between high-fertility herds and low-fertility herds was expected considering that herds were selected according to multiparous conception rate. The multiparous and the primiparous cows in the herds were kept in close proximity under identical environmental and management conditions, and the study animals were fed according to the same nutritional scheme; therefore, the effects of the influencing factors on reproductive indices of both parity groups in low-fertility herds and high-fertility herds would be expected to be similar. Looking at the differences in the overall conception rate between multiparous and primiparous cows it seems that primiparous cows were less sensitive to factors predisposing them to low fertility than were the multiparous cows. Therefore if the factors predisposing to low fertility are moderate, the overali conception rate of primipara may not be markedly impaired. The low correlation coefficients between primiparous and multiparous in low-fertility herds indicate that the negative influence of factors impairing fertility seems to be of major importance in low-fertility herds than in high-fertility herds. The overall conception rate of nulliparous, which were kept apart from the dairy cows and were fed according to a different nutritional scheme should not have been influenced by the selection of herds according to the overall conception rate of the multiparous cows. However, in this study the overall conception rate of nullipara was significantly lower in low-fertility herds than in high-fertility herds. Additionally, the low correlations between the overall conception rate of nullipara and primi-/multipara in high- and low-fertility groups of herds point to increasing fertility problems with the beginning of lactation and adaptation of nutrition to the lactating cows. Similar low correlations between nulliparous heifers and lactating cows were found by Ron et al. (1) in IsraeliHolsteins herds. In view of these findings, it is evident that general herd management and some possible factors not investigated in this study such as genetic effects and viral diseases may have a detrimental influence on the overall conception rate of all parity groups. The longer period from the first to last insemination in low-fertility herds was partially related to a high incidence of post-insemination anestrus, which was five to seven times higher in low-fertility herds than in high-fertility herds. Longer periods from the first to the last insemination together with a high percentage of herds having a high incidence of post-insemination anestrus in low-fertility herds, point to the serious reproductive disturbances found in low-fertility groups of herds. The difference in days open between the low-fertility herds and highfertility herds was small and approached significance only for multiparous cows. However, the parameter of days open was related only to the pregnant cows, and may therefore be strongly biased, especially within herds in which a high percentage of cows that did not conceive was culled. The shortcomings of the days open
400
Theriogenology
index or of the intercalving interval index for determining herds fertility status are emphasized by Bdhm (2), Noordhuizen (3) and Sonderegger (4). The polyfactorial character of the herd infertility syndrome is demonstrated by our data on 17 factors which were significantly different between low-fertility herds and high-fertility herds, and these findings are consistent with data of other researchers (5, 6, 7, 8, 9, 10, 11, 12, 13). Factors occurring more frequently in low-fertility herds were considered to be risk factors for infertility, while those occurring more frequently in high-fertility herds were considered to be fertility promoting factors. With the exception of phytoestrogens, which were found in low-fertility herds only, all the other factors were diagnosed in both fertility groups of herds. The total number of the risk factors was in high-fertility herds significantly lower than in low-fertility herds. Thus, it appears that risk factors have a cumulative influence on reproductive performance. Nutritional parameters had the highest influential effect on differences in reproductive performance between herds with similar production levels kept under similar environmental conditions. High protein levels were found to influence fertility adversely in high milk producing cows. This negative effect of high protein levels on reproductive performance is consistent with the findings of Brochart et al. (14), Canfield et al. (l-5), Frances and Mayer (16), Jordan and Swanson (17), Kaim et al. (18), Kaufmann (19) and Sonderegger (4), but differs from those of Carroll et al. (20) and Howard et al. (21). The energy/protein ratio fed during lactation and the dry period was connected with reproductive efficiency. Detrimental effects of either a low or high energy/protein ratio are also supported by Garibay Vila (22), Hafner and Schulz (23) and Busch et al. (24). Feeding high levels of energy at the end of lactation and dry period increased the average body score of dry cows significantly in low-fertility herds compared with high-fertility herds. Feeding of the same ration to all cows during the entire lactation period appeared to be connected with the risk of overconditioning toward the end of the lactation and during the dry period (25, 26, 27). The amount of dry matter fed during the second half of the lactation was higher in low-fertility herds than in high-fertility herds. A clear trend to overconsumption during the dry period and towards the end of lactation was observed in the low-fertility herds. Nevertheless, most of the dry cows were not obese, and a clear trend towards obesity was found only in 20% of low-fertility herds. Dry period overconditioning of cows can result in significantly high hepatic lipidosis, which can cause reproductive problems (27, 28, 29, 30). Although high levels of
Theriogenology
401
prepartum feeding may not result in overconditioning during the dry period, it does increase postpartum reproductive problems and elevates hepatic lipidosis severely (31, 32, 33, 34). In the herds surveyed in our study, the incidence of postpartum metabolic problems was low. Since biochemical examinations of the blood and liver were not included in our study, we can only assume that the low reproductive performance of low-fertility herds was influenced by hepatic lipidosis connected with high postpartum milk yield and with the high Ievel of nutrition during the dry period. An increase in body condition scores during the dry period among multiparous cows was connected with negative reproductive indices (with the exception of days from calving to first insemination). This was particularly evident for the wasted days index (days from the first to the last effective or ineffective insemination). This finding indicates that risk factors acting during the prepartum period influence reproductive performance for many months after calving (35, 36, 37, 38). Increased body condition in primiparous cows, as opposed to that in multiparous cows, contributed to more accurate reproductive indices. Early primiparous cows may have better body condition and fertility indices than primiparous cows that mature later; however, it could not be established if the early maturing cows become overconditioned in the dry period and thus may be exposed to more fertility problems in subsequent lactations in comparison with late maturing cows. Although differences in the absolute values of factors influencing fertility levels in high-fertility herds and low-fertility herds (see Table 4) were generally small, those factors were significantly correlated with herd fertility levels, thus demonstrating the high correlation between nutritional/metabolic factors and reproductive processes in high milk producing cows (39, 40). The negative influence of phytoestrogenic activity on reproductive performance that was found in this study is consistent with the data of others (41, 42, 43, 44). Therefore, examining suspected problem herds for the presence of phytoestrogens is recommended. Analysis of the data in this study strongly emphasizes the multifaceted character of influences on reproductive processes. In the course of this investigation, 17 different risk factors were identified, most of which were nutritional; approximately two-thirds of the differences existing between the overall conception rates of high- and low-fertility herds were explained by these nutritional factors. The longlasting effects of the fertility risk factors acting during the dry period on the postpartum reproductive performance, like that of overconditioning and the feeding of unbalanced rations, reflects the limited capacity of high milk producing dairy cows to return to the reproductive function disturbed by the postpartum period.
402
Theriogenology
This very fragile balance between nutrition and reproduction, apparently mediated through the linkage between metabolic and hormonal factors, is demonstrated by the findings that even relatively small differences in the level of protein, energy/protein ratio, body scoring during the dry period were connected with a marked decrease in reproduction indices. The connection between the number of fertility risk factors and the fertility rate within a herd demonstrates that herd fertility problems can be remedied by removing the risk factors. Extensive epidemiological studies combined with properly controlled experiments are needed to determine the thresholds of the nutritional factors contributing to both optimal milk yield and to high fertility in high milk producing dairy cows.
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