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ANIMAL GROWTH, PHYSIOLOGY, AND REPRODUCTION |
* Section of Torino, Istituto Sperimentale per la Zootecnia, I-10151 Torino, Italy and
and
Section of Breeding Technology, Istituto Sperimentale per la Zootecnia, I-00016 Monterotondo, Rome, Italy
Abstract
Relationships among plasma hormonal and metabolic variables in the last trimester of gestation in 59 Piedmontese dams (n = 15 heifers, n = 44 cows) and the calf birth weight (BWT) class of their offspring were investigated in seven herds. The BWT data were categorized as follows: >50 kg (BWT-A), 46 to 50 kg (BWT-B), 41 to 45 kg (BWT-C), and <41 kg (BWT-D). Blood samples were collected at 33, 36, and 39 wk of gestation. Packed cell volume (PCV) and plasma concentrations of insulin, estrone sulfate (E1SO4), NEFA, and creatinine were determined and correlated to BWT class. Creatinine:E1 SO4 ratio also was calculated. Duration of gestation was greater for dams producing a BWT-A calf than for the other BWT classes, and calf BWT was heavier (P < 0.001) for calves in the BWT-A vs. BWT-D class. The heaviest calf in BWT-A was associated with the highest calving difficulty score. Insulin and PCV values were not affected by week of gestation, whereas plasma E1SO4, NEFA, and creatinine content increased (P < 0.001) and creatinine:E1SO4 decreased (P < 0.001) during late gestation. Calf BWT class did not affect PCV value. Plasma E1SO4 concentrations were lower (P < 0.01) in BWT-D dams than the other dams, showing the greatest difference at 39 wk of gestation. At 36 and 39 wk of gestation, dams bearing BWT-C and BWT-D calves had a higher (P < 0.01) plasma insulin concentration than those bearing BWT-A and BWT-B calves. Plasma NEFA concentrations at 39 wk of gestation were higher (P < 0.05) in dams of calf BWT-A than in the other dams. We conclude that plasma E1SO4 level is a variable that can be used to monitor problems related to a small size calf. Conversely, the forthcoming birth of a calf with a heavy BW seems to be preceded by a pronounced increase in plasma NEFA level in the dam just a few days before calving.
Key Words: Beef Cow • Fetal Development • Hormones • Metabolites • Pregnancy
Introduction
Calves born to cows with dystocia were five times more likely to die neonatally than calves born without assistance (Azzam et al., 1993
). The major cause of dystocia in replacement heifers is relative fetal oversize or a disproportionate calf birth weight (BWT) in relation to the pelvic area of the dam (Basarab et al., 1993). Fetal size may depend on two factors: the genotype of the fetus (Bennett and Gregory, 1996; Varona et al., 1999) and the nutritional state of the dam, with special emphasis on the last trimester of gestation (Freetly et al., 2000).
Estrone sulfate (E1SO4) is the main estrogen in the plasma of the cow during the last trimester of gestation. Several authors (Henson et al., 1989; Echternkamp, 1993; Zhang et al., 1999) have reported a positive relationship between maternal plasma E1SO4 and/or estrone and calf BWT.
Additional tools to predict calf BWT may be researched by monitoring the maternal nutritional state during the last 3 mo of gestation. Insulin is an important metabolic hormone that affects nutrient utilization by the cow (Reynolds et al., 1990). The metabolic state of the cow may also be described through the levels of plasma metabolites related to the energy metabolism. For example, plasma levels of NEFA during the last 4 wk of gestation were higher in cows that calved heavy calves than in those that calved medium and light calves (Guedon et al., 1999).
The Piedmontese is an Italian breed selected for beef production characteristics. In recent years, there has been increased concern about the calving ability of this breed, due to a gradual increase in the incidence of dystocia (ANABORAPI, 1997). The objective of this study was to investigate, through a farm-scale survey, the relationships among some hormonal and metabolic variables in the last trimester of gestation of Piedmontese cows and the BWT class of their offspring, independent of the BW and other features of the dam.
Materials and Methods
General
A field survey was planned on the basis of the data from the National Association of Piedmontese Cattle Breeders (ANABORAPI) on 59 autumn-calving dams, including both primiparous (n = 15) and multiparous (n = 44) females. Pregnant cows were distributed among seven cattle herds of high genetic merit, but which had a high incidence of difficult calving. Dams were not genotyped for the myostatin allele; however, there was a high phenotypic expression of muscular hypertrophy in all the dams in the survey.
Before the survey started, we visited the farms with technicians of the local breeder’s association to obtain general information on herd management, focusing on the last trimester of gestation. Diets during the last trimester of gestation were similar and representative of the traditional feeding schedule of this breed in the Piedmont region of Italy.
Data concerning calving difficulty were recorded according to the ANABORAPI system and coded as follows: unassisted (CS1), easy assist (CS2), difficult assist (CS3), Caesarean section (CS4), and fetotomy (CS5). Calves were weighed within 6 h after delivery. Data for calf BWT were classified into four classes: >50 kg (BWT-A), 46 to 50 kg (BWT-B), 41 to 45 kg (BWT-C), and <41 kg (BWT-D).
Sampling
Blood samples were obtained from each cow at 33, 36, and 39 wk of gestation. A single blood sample was collected from the jugular vein, just before the morning distribution of feed (from 0700 to 0730), via venipuncture using 10-mL Li-heparin Venoject tubes (Terumo Europe, Leuven, Belgium). Blood samples were immediately placed into an ice bath, where they were stored until they were processed. All the herds were located in the Turin province near our institute, which permitted us to process the blood within 40 min after its withdrawal. After packed cell volume (PCV) determination using a hematocrit centrifuge, plasma was separated by centrifugation (2,850 x g for 20 min), and four subsamples were stored immediately at -20°C until analyzed.
Laboratory Analyses
Plasma samples were analyzed for insulin (insulin immune-radio-metric assay kit, Immunotech, Beckman Coulter, Czech Republic; intraassay and interassay CV were 3.4 and 4.0, respectively), for E1SO4 (DSL-5400 Estrone Sulfate RIA kit, Webster, TX; intraassay and interassay CV were 6.2 and 6.5, respectively), for NEFA (NEFA C-Test Wako, Wako Chemicals GmbH, Neuss, Germany), and for creatinine (Instrumentation Laboratory Test Creatinine, Instrumentation Laboratory Company, Lexington, KY).
Statistical Analysis
Calving data were analyzed as a single-factor ANOVA in a completely randomized design. A preliminary correlation analysis that estimated linear relationship among variables of some calving data, BWT, plasma hormones, and metabolite concentrations, was performed by week of sampling using the CORR procedure of SAS (SAS Inst., Inc., Cary, NC).
Normal distribution of blood variables was tested with the Shapiro-Wilk test (Hatcher and Stepanski, 1994) before further analysis. On this basis, data for PCV were determined to be distributed normally and were analyzed directly, whereas data for plasma E1SO4, insulin, NEFA, creatinine, and creatinine:E1SO4 were log-transformed to achieve the normal distribution of the data before further statistical analysis.
Time-sequence data were analyzed as a split-plot in a completely randomized design. Different statistical models were considered, including those with farm, calving order, calving score, and calf sex as main factors. However, on the basis of R2 and F values, the best model for all of the considered variables was that with calf BWT class (BWT-A, BWT-B, BWT-C, and BWT-D) and week of gestation (33, 36, and 39) as main factors. The effect of calf BWT class was tested against animal within calf BWT class, whereas week of gestation and calf BWT class x week of gestation interaction were tested against residual error. If a significant F-test were detected (P < 0.05), interactions were evaluated using the STDERR/PDIFF option of GLM in SAS.
Results
Calving Data
Results from calving data are reported in Table 1. All of the cows delivered a singleton calf (37 males and 22 females) between November 2000 and January 2001. Three male calves were stillborn (5.1% of total). A high number of males were born in the BWT-A class. This class was also characterized by a low presence of heifers. Duration of gestation was less for dams with a BWT-D calf than for dams in BWT-A and BWT-B classes (P < 0.05). Calving difficulty scores were higher (P < 0.05) for dams in the BWT-A vs. BWT-D class (x = 2.70 and 1.58, respectively); the heaviest calf BWT of BWT-A class was associated with the highest calving difficulty score. This means that the percentage of the calvings considered difficult (CS3, CS4, and CS5 calving difficulty score) was 56.5 vs. 8.3% in the BWT-A and BWT-D classes, respectively. The correlation coefficient between calf BWT and calving difficulty score was significant (r = 0.46; P < 0.0003).
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). This variable appeared to be constant and characteristic of the dam. At 39 wk, PCV value was correlated positively only with NEFA concentration (r = 0.33; P < 0.01).
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and Figure 1). Dams producing a calf with a BWT <41 kg (BWT-D) had lower plasma E1SO4 than BWT-A, BWT-B, and BWT-C dams at each week of sampling (P < 0.01). The greatest difference in plasma E1SO4 level between BWT-D class and the other classes was found at 39 wk of gestation. No significant interaction was detected between calf BWT and week of gestation.
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). Starting at 36 wk of gestation, dams bearing lighter calves (BWT-C and BWT-D classes) had higher (P < 0.01) plasma insulin concentration than those bearing heavier calves (BWT-A and BWT-B classes), as evidenced in Figure 2. Therefore, the relationship between calf BWT and plasma insulin content (log value) was negative at both 36 and 39 wk of gestation (r = -0.38 and r = -0.37 respectively; P < 0.01).
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and Figure 3). The effect of calf BWT class approached statistical significance (P = 0.09) with an increase in plasma NEFA concentrations at 39 wk of gestation; dams in calf BWT-A class tended to have higher values than those of dams in the other calf BWT classes (Figure 3). The log of this plasma variable was correlated (P < 0.05) with the log of the creatinine:E1SO4 ratio at 36 and 39 wk (r = -0.30 and r = -0.29, respectively) and with calf BWT at 39 wk of gestation (r = 0.26; P < 0.05).
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and Figure 4) and was higher (P = 0.004) in calf BWT-C class than in the other calf BWT classes. No significant interaction was evident. At 33 wk of gestation, the log of the plasma creatinine level showed a positive correlation with the log value of plasma E1SO4 (r = 0.32; P < 0.01); the correlation with the log of plasma insulin level was significant (P < 0.05) at 33 and 36 wk of gestation (r = 0.26 and r = 0.31, respectively).
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and Figure 5), decreasing (P < 0.0001) throughout late gestation, and showed higher (P = 0.001) values in BWT-D dams than in the other classes. The log of this ratio was related inversely (P < 0.01) with the log of plasma E1SO4 concentration at wk 33, 36, and 39 (r = -0.96, -0.98, and -0.97, respectively) at each time of gestation, but not with the log of plasma creatinine concentration.
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There are two main reasons to study the physiological relationships between blood variables in the dams and the BW of their offspring. First, a cow that calves a heavy offspring has a greater risk of experiencing dystocia. Second, a calf too light at birth may have more problems of vitality. The high calving difficulty scores in this survey were the consequence of our objective to investigate Piedmontese herds representative of this breed’s selection for meat production. These herds showed higher calving difficulty scores than those attainable in the studies of Carnier et al. (1997, 2000). Calving difficulty score in dams bearing calves of BWT-A was positively correlated with increased duration of gestation in this survey. This relationship between duration of gestation and calving difficulty agrees with the study of Carnier et al. (1997), in which they reported that increases in duration of gestation resulted in more difficult calvings in both Piedmontese heifers and cows. Guilbault et al. (1985) found that Holstein heifers that had been bred to a Brahman service-sire group and that calved the heaviest calves, had a mean duration of gestation 1 wk greater than those bred to Holstein or Angus bulls and that calved lighter calves.
Seventy-eight percent of offspring in BWT-A class were males. Only 33.3% of the dams in BWT-D class were heifers, confirming that BWT class was not strictly related to age of dam. Bennett and Gregory (2001) determined that calf (direct) genetic effects resulting in greater duration of gestation were associated both with increased calving difficulty score and birth weight. These authors suggested that the most accurate selection criteria for improvement of heifer calving difficulty are calving difficulty score and BWT traits. In addition, both characteristics can be measured early in life and in all calves, male and female.
Contrary to previous studies in which PCV decreased during late gestation until 2 wk prepartum (Collier et al., 1982; Shell et al., 1995; Abeni et al., 2001), PCV was unaffected by week of gestation in the present survey. This discrepancy was probably related to differences in environmental conditions. The present study was carried out entirely in autumn, whereas the previous studies were carried out during the stressful climate of summer (Collier et al., 1982; Shell et al., 1995; Abeni et al., 2001). Even if environmental and nutritional stressors may affect the dam’s PCV during late gestation (i.e., decreasing oxygen transport in the bloodstream and causing possible damage at the conceptus level), from these results, PCV of the dam did not seem to be related to physiological factors that might determine calf BWT. The relationship found during late pregnancy (i.e., at 39 wk) between PCV value and the corresponding trend in plasma NEFA could be interesting for detecting eventual problems related to an excess of mobilization of body lipid reserves of the dam. The reason for this relationship is unclear, and its confirmation and interpretation requires further investigation.
Estrone sulfate is well known as a good marker of fetal-placental activity (Echternkamp, 1993) because of the sulfation of the estrogen that takes place at the placentomal level (Hoffmann et al., 1979). The increase in plasma E1SO4 level in the Piedmontese dams during late gestation agrees with the results reported by several researchers in other breeds and under different feeding conditions (Abdo et al., 1991; Shell et al., 1995; Zhang et al., 1999). Generally, higher plasma E1SO4 and/or estrogen levels were correlated positively with calf BWT (Henson et al., 1989; Echternkamp, 1993; Zhang et al., 1999). In the present study, E1SO4 appeared to be a predictable indicator of dams bearing a future calf of low BWT; BWT <41 kg is considered a small size for the Piedmontese breed. Because more remains to be clarified concerning the possibility of utilizing this hormone to identify dams bearing a calf heavier than 50 kg (i.e., considered highly susceptible to calving difficulty in this breed), a possible tool to improve predictability of calf BWT could be represented by the ratio between E1SO4 and total estrogens, as suggested by S. E. Echternkamp (personal communication).
Data related to energy metabolism (insulin and NEFA) appear to be of interest for our purposes. Plasma insulin level was confirmed not to be affected by stage of gestation per se, as reported by Reynolds et al. (1990). Insulin became higher in BWT-C and BWT-D dams than in BWT-A and BWT-B dams starting at 36 wk of gestation. It is difficult to hypothesize a biological meaning of this result. However, it seems reasonable to speculate that a high level of plasma insulin could be a signal of relatively high energetic availability, probably due to a moderate weight gain of the fetus during the last month of pregnancy.
Results from NEFA data agree with those of Petit and Remond (1977), Hossner et al. (1997), and Guedon et al. (1999), and seem to confirm the implications of the insulin results obtained in the present study. This trial revealed a general increase in plasma NEFA level during the last 2 mo of gestation, with a trend for higher value at 39 wk in dams of calf BWT-A class (>50 kg). The increase in plasma NEFA level during late gestation might be due to an increased nutrient requirement caused by the growth of a heavy fetus. Therefore, body fat reserves may be mobilized and, as a consequence, plasma NEFA content increased close to the end of gestation (Bell, 1995). These suggestions agree with the insulin trend in dams bearing heavy calves (>46 kg); dams in BWT-A and BWT-B classes had significantly lower insulin than dams in BWT-C and BWT-D classes at 36 and 39 wk of gestation. This situation may be further promoted by a large size of the fetus relative to its dam; this could lead to a decrease in dry matter intake by the dam because of reduced space availability in the digestive tract caused by the size of the calf.
Few studies are available to compare to our results on plasma creatinine level in late gestation, but actual values recorded in this survey were typical for a double-muscle breed like Piedmontese (Masoero, 1982). The increased plasma creatinine level during late gestation could be due to higher muscular work for the movement of the dam bearing the growing fetus. Previous studies (Peterson and Waldern, 1981; Tainturier et al., 1984) have reported increased blood creatinine concentration throughout the last 6 mo of gestation in Friesian cows. The higher value for calf BWT-C class is not explainable and does not aid in clarifying the reasons of plasma creatinine variation in late gestation. Therefore, further research on this metabolite during late gestation is necessary. The ratio of creatinine:E1SO4 in plasma reflects the results from estrone sulfate data and does not seem to improve knowledge about relationships between the dam and its fetus during late gestation.
Implications
Plasma concentration of estrone sulfate is confirmed to be a variable for monitoring problems related to a small size calf. The forthcoming birth of a calf with a heavy body weight seems related with a metabolic state of the dam typical of a situation of energy mobilization (low plasma insulin and high plasma nonesterified fatty acid concentrations). Further studies will be necessary to understand whether different nutritional strategies during the second and third trimester of gestation might have an effect to achieve a desired class of birth weight of the offspring at calving.
Footnotes
1 This research was supported by a grant of Regione Piemonte Department of Agriculture (Italy). The authors give special thanks to S. E. Echternkamp for his suggestions in manuscript preparation and to M. Cravero for his veterinary assistance in blood sampling. 
2 Correspondence: Via Pianezza 115 (phone: +39 011 731689; fax + 39 011 731689; e-mail: giuseppe.bergoglio{at}isz.it).
Received for publication July 3, 2003. Accepted for publication October 14, 2003.
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group A), 46 to 50 kg (
group B), 41 to 45 kg (
group C), <41 kg (x group D). Pooled SEM was 0.56. dFrom wk 33 to 39, the mean of group D was less (P < 0.05) than those of the other groups that did not differ from each other.
