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Veterinaria México OA

versión On-line ISSN 2448-6760

Veterinaria México OA vol.3 no.1 Ciudad de México ene./mar. 2016 

Original Research Articles

Ovulation rate, prolificacy and pregnancy rate in goats treated with oral glycerol

Ubaldo Aguilar1 

Joel Hernández Cerón1  *

Yesmín Domínguez2

Carlos G. Gutiérrez1

1Departamento de Reproducción Facultad de Medicina Veterinaria y Zootecnia Universidad Nacional Autónoma de México Av. Universidad 3000, Ciudad de México 04510, México

2Centro de Enseñanza, Investigación y Extensión en el Altiplano Facultad de Medicina Veterinaria y Zootecnia Universidad Nacional Autónoma de México Av. Universidad 3000, Ciudad de México 04510, México


This study tested whether the oral administration of glycerol at the time of progestin removal and in the first 6 days of the estrous cycle increased the ovulation rate, prolificacy, and pregnancy rate in goats. Intravaginal sponges impregnated with fluorogestone acetate were inserted into 129 goats for 12 days; upon sponge removal, goats were randomly assigned to one of the two following treatment groups: the glycerol group (n = 65), which received an oral drench of 100 mL of glycerol upon sponge removal and was repeated on days 0, 2, 4, and 6 following estrus (estrus = day 0), and the control group (n = 64), which did not receive glycerol. The goats in estrus were mated, and their ovulation rate was determined by ultrasonography between days 8 and 12 of the estrous cycle. Pregnancy was diagnosed by ultrasonography on day 40, and the prolificacy was determined at birth. In 6 goats treated with glycerol and 5 controls, their insulin concentrations at 0, 2, 4, 8, and 12 h after the glycerol drench were determined by radioimmunoassay. The proportion of goats with multiple ovulations (glycerol = 71 vs control = 64) and the proportion of goats with multiple births (glycerol = 52 vs control = 56) were similar (P > 0.05) between treatments. Likewise, the pregnancy rate was similar (P > 0.05) between treatments (glycerol = 88 vs control = 85%). The insulin concentrations tended to be higher in goats treated with glycerol (P = 0.08). In conclusion, an oral drench of 100 mL of glycerol at the time of progestin withdrawal and in the first 6 days of the estrous cycle did not increase the ovulation rate, prolificacy, or pregnancy rate in goats.

Keywords: Ovulation rate; Prolificacy; Glycerol; Insulin; Goats


Se probó si la administración oral de glicerol, al momento de retirar el progestágeno y durante los primeros seis días del ciclo estral, incrementaba la tasa de ovulación, la prolificidad y la tasa de gestación en cabras. Se insertaron esponjas intravaginales con acetato de fluorogestona a 129 cabras por 12 días; al retirar la esponja se asignaron al azar a uno de dos tratamientos: glicerol (n = 65) recibió 100 mL de glicerol por vía oral, mismo tratamiento que se repitió los días 0, 2, 4 y 6 (estro = día 0), y testigo (n = 64), el cual no recibió glicerol. Las cabras en estro recibieron monta. Entre los días 8 y 12 del ciclo estral, se determinó la tasa de ovulación mediante ecografía. El diagnóstico de gestación se realizó mediante una ecografía el día 40 y la prolificidad se determinó al parto. En seis cabras tratadas con glicerol y cinco testigos, se determinaron las concentraciones de insulina mediante radioinmunoensayo a las 0, 2, 4, 8 y 12 h después de la ingestión de glicerol. La proporción de cabras con ovulación múltiple (glicerol = 71 vs testigo = 64) y la proporción de cabras con parto múltiple (glicerol = 52 vs testigo = 56) fueron similares (P > 0.05) entre los tratamientos. De manera similar, la tasa de gestación fue igual (P > 0.05) entre los tratamientos (glicerol = 88 vs testigo = 85%). Las concentraciones de insulina tendieron a ser mayores en las cabras tratadas con glicerol (P = 0.08). Se concluye que la administración oral de 100 mL de glicerol al momento de retirar el progestágeno y durante los primeros seis días del ciclo estral, no incrementó la tasa de ovulación, la prolificidad, ni la tasa de gestación en cabras.

Palabras clave: Tasa de ovulación; Prolificidad; Glicerol; Insulina; Cabras


An increase in the ovulation rate and prolificacy in small ruminants has been achieved in an efficient way through hormone treatments and by increasing the energy content in the diet (flushing). Although the flushing mechanism is not yet fully understood, the evidence indicates that its effects are produced at the ovarian level; furthermore, they are independent of gonadotropin concentrations and are associated with increases in the blood glucose and insulin levels (Downing et al., 1995; Muñoz-Gutiérrez et al., 2004; Dupont et al., 2014).

In sheep, short-term supplementation with lupin grain, a legume with a high metabolizable energy and protein content, can increase ovulation rates. Short-term supplementation with lupin grain stimulates folliculogenesis and increases ovulation rates, without inducing changes in body weight and condition (Scaramuzzi et al., 2006). Glucose and insulin may influence the ovulation rate by stimulating follicle development, resulting in a higher number of follicles capable of responding to gonadotropin stimulus (Gutiérrez et al., 1997; Viñoles et al., 2005). Furthermore, glucose and glucosamine stimulate follicle steroidogenic capacity by increasing insulin-like growth factor type I (IGF-I) activity (Muñoz-Gutiérrez et al., 2004). Studies performed in goats show that an increase in insulin, either induced by diet or by insulin administration, increases the ovulation rate (Suguna et al., 2009; Zabuli et al., 2010).

The administration of glycogenic solutions can cause an increase in the blood glucose and insulin concentrations. In sheep, short-term treatments with glycerol and propylene glycol have been used to increase ovulation rates. Rodriguez Iglesias et al. (1996) were able to increase the ovulation rate in seasonally anovulatory ewes through the oral administration of 100 mL of a glycerol and propylene glycol solution, which were administered immediately before ram exposure. Gutierrez et al. (2011) observed increased serum glucose concentrations, insulin, and ovulation rates with a single oral dose of 300 mL of glycerol during the induction of luteolysis with PGF2α in Pelibuey sheep. In the same study, a similar effect on the ovulation rate with a single oral dose of 100 mL of glycerol was achieved.

Moreover, insulin promotes early embryonic development. In vitro insulin exerts a mitogenic and an antiapoptotic effect on embryos (Byrne et al., 2002; Augustin et al., 2003), resulting in an increased proportion of embryos reaching the blastocyst stage. Additionally, high insulin concentrations negatively affect embryonic development in cattle (Fouladi-Nashta et al., 2006) and sheep (Carrera-Chávez et al., 2014). Furthermore, a positive effect from insulin on luteal function has been observed. In a goat study, insulin was associated with higher concentrations of progesterone during pregnancy (Suguna et al., 2009). High levels of progesterone are associated with accelerated embryonic development (Garret et al., 1988), which could translate into fewer embryonic losses. In dairy cows, the administration of 1 L of oral glycerol during the first 6 days post-insemination increases blood insulin levels and increases the pregnancy rate (Ortega et al., 2010). Therefore, this study tested whether the oral administration of 100 mL of glycerol, at the time of progestin removal and in the first 6 days of the estrous cycle, increased the ovulation rate, prolificacy, and pregnancy rate in goats.

Materials and methods


This study was conducted in an experimental station at the Facultad de Medicina Veterinaria y Zootecnia of Universidad Nacional Autónoma de México (UNAM), located in Tequisquiapan, Querétaro, at a latitude of 20°31’21” N and at 1881 m above sea level. The regional climate is temperate and semi-arid, with an average temperature of 17.5º C and an average annual rainfall of 512 mm (García, 1981). The experiment was carried out from September to November, which corresponds to the reproductive season of goats in Mexico (Arvizu et al., 1995).


In this experiment, 129 crossbreed (Boer-Alpine French) cycling goats (22 doelings and 107 does varying in parity) with a body condition score between 2 and 3 were included (Russel et al., 1969). The goats were confined and fed a diet based on alfalfa hay, corn silage, and concentrate according to NRC requirements. This experiment was approved by the Consejo Académico del Posgrado en Ciencias de la Producción y de la Salud Animal from UNAM.


In all goats, an intravaginal sponge impregnated with 45 mg of fluorogestone acetate (FGA; Chronogest; MSD Animal Health, Mexico; Intervet México, S.A. de C.V., Huixquilucan, Estado de México, México) was inserted and remained in situ for 12 days. When the sponge was removed, a luteolytic dose of sodium cloprostenol (Celosil; MSD Animal Health, Mexico) was administered. Upon sponge withdrawal, the goats were randomly assigned to one of the following treatment groups: the glycerol (n = 65) group, which received an oral drench of 100 mL of glycerol repeated on days 0, 2, 4, and 6 following estrus (estrus = day 0), and the control (n = 64) group, which did not receive glycerol. Males fitted with an apron performed estrus detection. Females in estrus were mated to males of proven fertility.

Between days 8 and 12 post-mating, the ovulation rate was determined via a transrectal ultrasound exam by counting the number of corpora lutea; for this purpose, a 7.5 MHz linear transducer (Aloka, Co., Ltd., Tokyo, Japan) was used, which was adapted to a rigid support to allow for handling (Gutierrez et al., 2011). The pregnancy rate was determined by ultrasonographic pregnancy diagnosis on day 40 after service. Prolificacy was determined at birth (Figure. 1).

Figure 1: A schematic overview of the treatments. 

Blood sampling and sample processing

To determine blood levels of progesterone and insulin, 6 goats were treated with oral glycerol and 5 controls were randomly sampled. Blood samples for progesterone quantification were taken daily between days 1 and 17 of the estrous cycle. Two goats in the control group presented with short cycles; therefore, they were not included in the progesterone statistical analysis. On day 4 of the estrous cycle, sampling was conducted in order to determine blood insulin levels induced by the oral administration of glycerol. The first sample was taken before treatment (0 h), and the next samples were taken at 2, 4, 8, and 12 h after the glycerol drench.

Blood samples (10 mL) were obtained by puncture of the jugular vein using Vacutainer® tubes containing 100 µL of sodium citrate. The blood samples were centrifuged at 1500 x g for 10 min to separate the plasma, which was subsequently stored at -20 °C until analysis. The progesterone and insulin concentrations were determined by solid-phase radioimmunoassay (Coat-A-Count®, RIA kit, DPC; USA). In the case of progesterone, the assay sensitivity was 0.1 ng/mL with an intra-assay variation coefficient of 4.2%, while the insulin sensitivity was 0.052 ng/mL, with an intra-assay variation coefficient of 3.3%.

Statistical analysis

A logistic regression model was used to determine the effect of oral glycerol treatment on the percentage of goats with multiple ovulations and multiple births. Likewise, the effect of parity (primiparous and multiparous) and its interaction with treatment was tested by logistic regression [SAS version 9.2 (SAS Institute Inc., Cary, NC)]. The ovulation rate and prolificacy were compared by the Mann-Whitney U test, in which the effect of treatment and its interaction with parity were considered. The differences in the progesterone and insulin concentrations between treatments were tested by ANOVA for repeated measurements; the model included treatment, time, and their interactions. In all cases, P < 0.05 was considered to be significantly different and P ≤ 0.10 was considered to be a tendency.

Results and Discussion

The oral administration of 100 mL of glycerol at the time of progesterone withdrawal did not increase the ovulation rate, and the proportion of goats with multiple ovulations or multiple births was similar between treatments (Tables 1 and 2). The ovulation rate [glycerol= 1.84 ± 0.64 vs control=1.80 ±0.72 (mean ± standard deviation)] and the prolificacy [glycerol= 1.58 ± 0.61 vs control=1.60 ±0.64 (mean ± standard deviation)] were similar between treatments. These results are different from those observed in sheep by Rodriguez Iglesias et al. (1996) and Gutierrez et al. (2011). The reason the treatment did not have a favorable effect on the ovulation rate may be related to the metabolic response to the oral glycerol doses. The 100 mL glycerol dose was determined based on the results obtained in sheep by Gutierrez et al. (2011); in their study, the administration of 100 mL glycerol caused an increase in the ovulation rate similar to the one obtained with 300 mL. For this reason, the administration of 100 mL was chosen. In the present study, serum insulin concentrations were not affected by the treatment (P = 0.11), but there was an interaction between the treatment and time (P = 0.08). Thus, insulin concentrations tended to be higher within 2 and 4 h post-treatment (Figure 2). Likely, this slight increase in insulin concentrations was not enough to improve the ovulation rate. The cause of the variation in response to the same glycerol dose observed between sheep and goats is unknown. Studies evaluating glycogenic solutions have been performed in sheep and cattle, but not in goats (Rodriguez-Iglesias et al., 1996; Ortega et al., 2010; Gutierrez et al., 2011). Although these 3 species are ruminants, they present differences in their digestive function and their use of forages. Goats have physiological adaptations that allow them to leverage high fiber feeds more efficiently (Silanikove, 2000). Therefore, they may be less sensitive to variations in the quality and quantity of offered feeds. Oral glycerol is used as a substrate in rumen fermentation from which propionate can be obtained. However, it can also be absorbed directly as glycerol through the rumen mucosa, which will be converted later into glucose in the liver (Trabue et al., 2007). Although this metabolic pathway is the same in ruminants, its efficiency in triggering insulin secretion may be different between species; this could explain, in part, the success of the treatment in increasing the ovulation rate in sheep as well as its failure in goats. The results of this study promote the development of future studies in goats to evaluate different glycerol doses, until the dose that triggers an optimal response in serum insulin is determined.

Table 1: Percentage of goats with multiple ovulations that received an oral drench of 100 mL glycerol. 

Table 2: Percentage of goats kidding more than one kid that received an oral drench of 100 mL glycerol. 

Figure 2: Average insulin concentrations (± standard error) in goats treated with 100 mL of glycerol () and controls (). Treatment by time interaction: P = 0.08. 

Furthermore, this study proposed that the oral administration of glycerol during the first days of embryo development (days 0, 2, 4, and 6 of the estrous cycle) favors embryonic survival, which would increase the proportion of pregnant goats and prolificacy. This hypothesis was based on the expected effect of glycerol on insulin concentrations and the effects of insulin on embryonic development. Studies performed in vitro and in vivo show that insulin improves embryonic development by increasing cell proliferation and decreasing apoptosis (Augustin et al., 2003; Suguna et al., 2009). Meanwhile, low insulin concentrations adversely affect embryonic development and interferon tau production (Thatcher et al., 1995). Furthermore, in dairy cows, an increase in insulin concentrations induced by the oral administration of 1 L of glycerol during the first 6 days of embryonic development (days 0, 2, 4, and 6) has been shown to improve pregnancy rates (Ortega et al., 2010). In the present study, however, the pregnancy rate (glycerol = 88 vs control = 85%) and the proportion of multiple births were similar between treatments (P > 0.05; Table 2). The lack of effect on prolificacy and pregnancy rate observed in this study was probably due to the marginal increase in insulin concentrations after the oral administration of 100 mL of glycerol. Furthermore, the pregnancy rate obtained in both groups was high, which makes it more difficult to identify a positive effect from any treatment aimed at improving fertility. Parity was observed to have an effect on ovulation rate and prolificacy; however, there was no interaction between the treatment and parity (Tables 1 and 2; P > 0.1).

The administration of oral glycerol during the first days of the estrous cycle may favor embryonic development and conception rate by increasing serum progesterone concentrations. This hypothesis is based on studies in cattle in which insulin increases circulating progesterone concentrations (Spicer y Echternkamp, 1995; Cooke et al., 2012). In this study, nonetheless, progesterone concentrations between 1 and 17 days post-mating were similar between treatments, and no interaction was observed between the treatment and time (P > 0.05; Figure 3).

Figure 3: Average concentrations of progesterone (± standard error) in goats treated with 100 mL of oral glycerol () and controls () (P > 0.05). 

The good body condition of the goats used in this study, as well as the season in which the treatment was applied, may have influenced the lack of a positive response to glycerol administration. The goats received a diet that met the NRC requirements, and they had a body condition between 2 and 3 at the beginning of the experiment, which is reflective of the conditions associated with a high pregnancy rate and high prolificacy and are similar to those obtained consistently within the flock. Conversely, this study was completed during the height of the reproductive period, which contributed to the excellent response in fertility. Future experiments should be conducted in conditions in which the fertility and prolificacy are diminished, such as in cyclicity induction programs during anestrus or in marginally nourished goats; in these circumstances, the supplementation proposed in this study may improve fertility. Treatments exist that do not increase pregnancy rates globally, but rather do so in subgroups of animals. In a previous study conducted by our group, for example, bovine recombinant somatotropin only increased pregnancy rate in goats in anestrus, as well as only increased prolificacy in primiparous goats, who naturally tend to have a lower pregnancy rate and prolificacy (Hernández y Gutiérrez, 2012).


In conclusion, the oral administration of 100 mL of glycerol at the time of progestin withdrawal and in the first six days of the estrous cycle did not increase the ovulation rate, prolificacy, or pregnancy rate in goats.


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Part of this study was funded by project PAPIIT IN22235 of UNAM, Mexico.


The authors are grateful to the workers and technicians of the experimental station for providing the facilities, animals, and constant support during the study.

Received: October 12, 2015; Accepted: March 16, 2016

*Autor para correspondencia: Tel: +52 5 5622-5860 Correo electrónico:

The authors declare that they have no conflicts of interest.

Ubaldo Aguilar performed the experiment and analyzed the results. Yesmín Domínguez performed the experiment. Joel Hernández Cerón and Carlos G. Gutiérrez designed the experiment, analyzed the results and wrote the manuscript.

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