# Energy Supply - Energy Required - Energy Balance

** Background:** In previous class periods we have discussed how NRC predicts the energy intake (Mcal/d). This activity focuses on how to calculate energy requirements and what happen if/when energy requirement is not equal to energy intake.

*Instructions:*** Part I:** First, let’s decide what factors should be included or not in the calculation of energy requirements. Complete the Table indicating “yes” if a factor should be included) or “no” if a factor should be assumed to be negligible or equal to “zero” for each scenario presented in the Table below. MAINT = maintenance; GRTH = body growth still needed to reach mature body weight; GRAZ = Physical activity associated primarily with grazing activity and walking of lactating cows; MILK = milk production; PRGCY = pregnancy; and BWGN = body weight gain.

Scenario | MAINT | GRTH | GRAZ | MILK | PRGCY | BWGN |
---|---|---|---|---|---|---|

1. A 3^{rd} lactation 1400-lb Holstein cow 49 days in milk (DIM) producing 106 lbs of milk with 3.4% fat. Her BCS is 3.5 but she is losing 0.4 kg of body weigh per day, She is fed a total mixed ration (TMR) in a free stall barn |
Yes | No | No | yes | No | No |

2. A 1^{st} lactation 1000-lb Jersey cow in pasture after dried off and days carrying calf = 220 which will weigh 80 lbs at birth |
Yes | Yes | No (not milking) | No | Yes | No |

3. A 2^{rd} lactation Brown Swiss cow of 1300-lbs, 220 (DIM) in a late lactation pen of multiparous cows producing 80 lbs of milk with 3.7% fat. Her BCS is 3.5 and she is gaining 0.1 kg of body weight per day. She is 150 days pregnant and she is fed a TMR. |
Yes | No (ideally Yes) | No | Yes | No | Yes |

4. A 5^{th} lactation 1300-lb Brown Swiss 330 DIM, producing 40 lbs of milk with 4.2% fat. Her days carrying calf is 210 of a 100-lb calf at birth. She walks 2 km/d of hilly land between the parlor and the pasture. |
Yes | No | Yes | Yes | Yes | No |

**Now, let's calculate the energy requirement (Mcal/d) for each of the factors and total daily energy requirement using the equations listed in Table 1 of today's reading. Do do so easily, use the Energy-System-Spreadsheet (Go to "requirements" tab).**

__Part II:__Scenario | MAINT | GRTH | GRAZ | MILK | PRGCY | BWGN | TOTAL |
---|---|---|---|---|---|---|---|

1. A 3^{rd} lactation 1400-lb Holstein cow 49 days in milk (DIM) producing 106 lbs of milk with 3.4% fat. Her BCS is 3.5 but she is losing 0.4 kg of body weigh per day, She is fed a total mixed ration (TMR) in a free stall barn |
10.1 | 0 | 0 | 33.2 | 0 | 0 | 43.3 |

2. A 1^{st} lactation 1000-lb Jersey cow in pasture after dried off and days carrying calf = 220 which will weigh 80 lbs at birth |
7.9 | 1.6 | 0(not milking) | 0 | 2.5 | 0 | 11.9 |

3. A 2^{rd} lactation Brown Swiss cow of 1300-lbs, 220 (DIM) in a late lactation pen of multiparous cows producing 80 lbs of milk with 3.7% fat. Her BCS is 3.5 and she is gaining 0.1 kg of body weight per day. She is 150 days pregnant and she is fed a TMR. |
9.6 | 1.0(ideally Yes) | 0 | 26.1 | 0 | 0.6 | 37.2 |

4. A 5^{th} lactation 1300-lb Brown Swiss 330 DIM, producing 40 lbs of milk with 4.2% fat. Her days carrying calf is 210 of a 100-lb calf at birth. She walks 2 km/d of hilly land between the parlor and the pasture. |
9.6 | 0 | 7.8 | 13.9 | 2.9 | 0 | 34.2 |

**To make sure we understand how "energy balance" works, answer the following two questions considering our scenario 1 (3**

__Part III:__^{rd}lactation Holstein cow) and scenario 4 (5

^{th}lactation Brown Swiss cow).

__Question 1:__ Which of the two cows is in positive energy balance and which one is in negative energy balance and why?

__Question 2:__ Knowing that the predicted dry matter intake (as calculated by the NRC equation) of the Holstein and the Brown Swiss cow is 53.5 lb/d and 48.8 lb/d, respectively and assuming that the NE concentration of their respective diet is 0.77 Mcal/lb DM and 0.70 Mcal/lb DM, respectively, determine Energy Intake, and show how the total energy requirement (calculated above) is equal to the energy supply *(so that we respect the first law of thermodynamic)*.

Holstein cow is losing 0.4 kg body weight per day at a BCS of 3.5. From Table 3 of the reading, we can calculate the amount of energy she is getting from the tissue mobilization: 0.4 kg/d x 5.1 Mcal/kg = 2.0 Mcal/d.

Thus for this Holstein Energy required (43.3 Mcal/d) = Energy intake (41.2 Mcal/d) + Energy from body tissue mobilization (2.0 Mcal/d)

Brown Swiss cow energy intake = 48.8 lb/d DMI x 0.70 Mcal/lb DMI = 34.2 Mcal/d

Brown Swiss cow is not gaining weight nor losing weight and thus no energy is required nor supplied by change in body weight

Thus for this Brown Swiss cow Energy required (34.2 Mcal/d) = Energy intake (34.2 Mcal/d).