52a Reunião Anual da Sociedade Brasileira de
Zootecnia
Zootecnia: Otimizando Recursos e Potencialidades
Belo Horizonte – MG, 19 a 23 de Julho de 2015
Efeitos da glicerna no balanço de nitrogênio, síntese de proteina microbiana e metabólitos sanguíneos em
vacas leiteiras1
Pablo Gomes de Paiva2, Fernanda Carolina Ramos dos Santos3, Arthur G.V.B. Costa3, Vitor Chiaroni Galvão3,
Carlos Eduardo Cardoso Consentini3, Guilherme Fonseca Cabral4, Francisco Palma Rennó3
1
Parte de da tese de doutorado do primeiro autor.
Doutorando do Programa Pós-Graduação em Zootecnia – FCAV/UNESP, Jaboticabal, Brazil. e-mail: [email protected]
3
Departamento de Nutrição e Produção Animal, Escola de Medicina Veterinaria e Zootecnia – USP, Pirassununga, Brazil. e-mail:
[email protected]
4
Faculdade de Zootecnia e Engenharia de Alimentos – USP, Pirassununga, Brazil.
2
Resumo: O objetivo deste estudo foi avaliar os efeitos da inclusão de glicerina a dieta em substituição milho grão
sobre o balanço de nitrogênio, síntese de proteina microbiana e metabólitos sanguíneos de vacas leiteiras. Foram
utilizadas vinte e quatro vacas da raça Holandesa (184 ± 50 DEL; 29,38 ± 0,89 kg/dia/leite; 594 ± 39 kg de PC)
distribuidas em seis 4 × 4 quadrados latinos, com períodos experimentais de 21 dias. As vacas foram distribuídas
dentro de cada quadrado para receber uma das seguintes dietas: Controle (0% de glicerina); 7% de glicerina; 14% de
glicerina; e 21% de glicerina adicionado a dieta em substituição ao milho moído. Os dados foram analizados com
PROC MIXED do SAS 9.0, sendo incluídos no modelo dieta, período e quadrado como efeitos fixos e animal dentro
de quadrado como efeito aleatório. As concentrações de glicose aumentaram com inclusão de glicerina. Houve efeito
quadrático de glicerina no nitrogênio sanguíneo, com menores valores nas dietas contendo 7 e 14% de glicerina. Não
houve efeito da glicerina sobre as enzimas do figado, aspartato succiniltransferase e gama glutamil tranferase. O
consumo de nitrogenio (N), N urina, N fecal, N no leite e eficiência de uso do nitrogênio foi reduzida pela adição de
glicerina as dietas. Dietas contendo altos níveis de glicerina afetaram o balanço de nitrogênio e alteraram metabólitos
sanguíneos em vacas no terço-médio de lactação.
Palavras–chave: biocombustíveis, energia, glicerol, produção de leite
Effect of glycerin on nitrogen balance, microbial protein synthesis and blood metabolites of lactating dairy
cows
Abstract: The aim of this study was to evaluate the effects of glycerin in replacing corn grain on nitrogen balance,
microbial protein synthesis and blood metabolites of lactating dairy cows. Twenty-four Holstein cows (184 ± 50
DIM; 29,38 ± 0,89 kg/d milk yield; 594 ± 39 kg BW) were assigned in a 4 × 4 Latin square design, with 21 days of
experimental periods. Cows were assigned within each square to receive one of the following diets: Control (0%
glycerin); 7% of glycerin; 14% of glycerin; and 21% glycerin added to diets on replacing ground corn grain. Data
were analyzed with PROC MIXED procedure of SAS 9.0 with a model that included diet, period, and square as fixed
effects and animal within square as a random effect. Glucose concentration was increased by glycerin. Glycerin has
a quadratic effect on blood urea nitrogen, with lower values in the diets that contained 7 and 14% of glycerin. There
was no effect of glycerin on aspartic succinyltransferase and gamma-glutamyl transferase liver enzimes. Nitrogen
intake, urine N, fecal N, milk N, and efficiency of N use were decreased by glycerin addition in the diet. Diets
containing high glycerin levels affected the nitrogen balance and change blood metabolites in mid-lactation dairy
cows.
Keywords: biofuls, energy, glycerol, milk production
Introduction
The growth of the biodiesel industry has increased demand for grain, reducing availability for use in animal
feed and therefore creating a need for alternative feed sources. Glycerin has been considered a potential energy source
in replacing starch in ruminant nutrition (Donkin et al., 2009; Carvalho et al., 2011). However, some studies had
reported negative effects of glycerin on dry matter intake (DMI) and nutrient digestibility that have limited its
inclusion to 10 and 15% of the diet (Donkin, et al., 2009; Shin et al., 2012; Carvalho et al., 2011). Thus, this fact
could be affect nitrogen metabolism and blood metabolites of dairy cows. Therefore, the aim of this study was to
evaluate the effects of glycerin in replacing corn grain on nitrogen balance, microbial protein synthesis and blood
metabolites of lactating dairy cows.
Material e Methods
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52a Reunião Anual da Sociedade Brasileira de
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Zootecnia: Otimizando Recursos e Potencialidades
Belo Horizonte – MG, 19 a 23 de Julho de 2015
Twenty-four multiparous Holstein cows averaging 184 ± 50 DIM, 29,38 ± 0,89 kg/d milk yield and 594 ± 39
kg BW were assigned to squares based on initial milk yield and body weight, and randomly assigned within square
to treatment sequence in six 4 × 4 Latin square design. Each experimental period had 21 d, with 14 d of adaptation
and 7 d for sample collection. The cows were assigned within each square to receive 1 of 4 experimental diets,
formulated according to the NRC (2001), as follows: 1) control (without added glycerin), 2) 7% glycerin (DM basis),
3) 14% glycerin (DM basis) and 4) 21% glycerin (DM basis) replacing ground corn grain in the diets. The forage
used during the experiment was corn silage, in 50:50 forage: concentrate ratio. Cows were fed twice daily at 0700
and 1300 h to supply 105-110% of expected intake. Animals were housed in individual pens of 17.5 m2 with sand
beds and forced ventilation, had free access to water, and were mechanically milked twice daily at 0600 and 1600 h.
Feed intake were recorded daily as the difference between feed offered and refused. On d 16 to 18 of each
period, fecal samples were taken from each cow, twice daily after milking, comprising a composite sample.
Indigestible acid detergent fiber (iADF) was used as an internal marker to estimate fecal excretion.
Blood samples were collected on d 15 of each period from the coccygeal vessels before the morning feeding.
Blood samples were centrifuged at 3000 × g for 10 min and plasma was separated and stored frozen at -20oC until
analysis. Analyses were performed using colorimetric commercial kits (Glucose: cat. no. K-082; Urea: cat. no. K056; AST: cat. no. K-048; GGT: cat. no. K-080, all from the Bioclin, Belo Horizonte, Brazil).
On d 16 and 17 of each period, spot urine sample were collected from each cow 4 h after morning feeding,
and then analyzed for creatinine, uric acid and allantoin for estimated microbial protein synthesis (Chen and Gomes,
1992). Total N in urine samples was determined (method 984.13; AOAC, 2000). The N balance was obtained by
difference between total N intake and N excreted in the urine and feces, and secreted in the milk.
The data were analyzed with PROC MIXED (Statistical Analysis System for Windows 9.0 - SAS - SAS
Institute Inc., Cary, USA), and model included diet, period and square as a fixed effect, and animal within square as
a random effect. Difference was declared significant at P<0.05.
Results and Discussion
Glucose concentration were linearly increased (P<0.05), from 7% of glycerin inclusion in the diet (Table 1).
Blood glucose concentration was decreased (Carvalho et al., 2011), unchanged (Kass et al., 2012; Shin et al., 2012),
or increased (Donkin et al., 2009) when glycerin was added up to 15% of the diet. This differences between studies
could be related to the purity of glycerin, amount glycerin added, and the time of blood sampling relative to meal
time.
Table 1 - Effects of glycerin levels on blood metabolites, nitrogen balance and microbial protein synthesis in lactating
dairy cows
Inclusion of glycerin, % of DM
P-value
Item
SEM
0
7
14
21
LIN
QUA
78.84b
83.93a
83.96a
86.40a
BUN, mg/dL
36.95
a
32.50
b
32.26
b
ab
0.74
<0.01
0.30
0.76
0.13
0.01
AST,2 U/L
63.91
62.68
61.07
60.41
1.12
0.09
0.59
29.77
30.23
29.59
32.24
0.83
0.08
0.20
584.19a
587.50a
575.15a
559.05b
a
8.59
0.04
0.30
a
b
b
4.52
<0.01
0.49
Blood metabolites
Glucose, mg/dL
1
3
GGT, U/L
33.36
Nitrogen Balance
Intake of N, g/d
Urine N, g/d
193.25
Fecal N, g/d
158.23a
155.47a
139.34b
127.38c
3.21
<0.01
0.23
a
b
b
c
2.51
<0.01
0.83
0.41
<0.01
0.15
67.1
0.20
0.57
Milk N, g/d
136.52
4
a
N efficiency
23.69
Microbial CP, g/d
2446
189.65
126.78
22.00
b
2415
163.95
130.15
22.48
b
2250
169.73
121.38
22.08
b
2323
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52a Reunião Anual da Sociedade Brasileira de
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Zootecnia: Otimizando Recursos e Potencialidades
Belo Horizonte – MG, 19 a 23 de Julho de 2015
a,b,c
1
Least squares means within a row with different superscripts differ (P<0.05).
BUN= blood urea nitrogen.
2
AST= Aspartic succinyltransferase.
3
GGT= Gamma-glutamyl transferase.
4
Nitrogen efficiency = 100 × milk N (g/d) / N intake (g/d).
The AST and GGT concentration were similar between treatments (P>0.05), but these values are within the
standard range reported for lactating dairy cows (Kaneko et al., 1997), and it’s a positive factor because these
parameters help to monitoring the metabolic status of dairy cows. Glycerin has a quadratic effect on blood urea N
(P<0.05), with lower values in the diets that contained 7 and 14% of glycerin. Daily N intake, urine N, fecal N, milk
N and efficiency of nitrogen use were decreased linearly (P<0.05), especially when glycerin was added up to 21% of
the diet. The reduction in BUN concentration is consistent with efficiency of nitrogen use, and this fact might be
related the effects of glycerin onvDMI. Shin et al. (2012) reported a quadratic effect on DMI in dairy cows fed corn
silage or cottonseed hull based diets, when glycerin was included up to 10% of diet. In contrast, glycerin added at
15% of the diet increased (Kass et al., 2012) or did not change DMI of mid-lactation dairy cows (Donkin et al., 2009).
Indeed, in this study the inclusion of glycerin did not affect microbial N synthesis (P>0.05). Likewise, microbial
protein synthesis was not impaired when glycerin was included up to 15% of the diet (Donkin et al., 2009; Shin et
al., 2012).
Conclusions
Diets containing high glycerin levels affected N balance and change blood metabolites of mid-lactation dairy
cows.
Acknowledgements
The authors thank the University of São Paulo (USP) and Dairy Cattle Research Laboratory for providing the
infrastructure necessary for this study. The author thank for scholarship support for P. G. Paiva was from Coordenação
de Aperfeiçoamento de Pessoal de Nível Superior (CAPES; Proc. n. BEX3664/14), Ministério da Educação, Brazil.
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