Friday, August 14, 2015

Life support - Pigs and Cattle

This is a follow-on to the previous post about raising animals for food. I won't go into detail about background issues like I did last time, I'll just dive right into the numbers and then compare.

To review, on a per kg ag waste basis we can produce one of:
490 g edible insects
290 g chicken eggs
140 g chicken
140 g catfish or tilapia
100 g rabbit

As a cheat sheet, here are my results for this post:
 90 g pork
 16 g beef + 1.094 kg cow's milk

I'll try to follow up with goats and sheep in a later post, since both produce milk as well as meat. This post turned out to be more complex than I expected since the beef section turned into sort of a lifecycle analysis rather than something I could just look up. Something else worth mentioning is that while growing plants in space can push the limits of productivity beyond what we see on Earth, raising animals puts us firmly into the realm of average at best.

 I know people who treat bacon as almost a religious observance. My youngest is addicted to ham. Sausage, chops, loin, pulled pork; there's plenty to enjoy on a pig.

 The FCR for pigs can be from 2.8 to about 4 depending on feed quality and conditions. Here's a detailed post covering pigs with an FCR of 3.8 and very good yield. Here's a feed budget sheet for raising pigs that hits 3.03, though the authors note that 3.3 is much more likely. Both of these results are using grains as feed, but grains are some of the lowest producers in terms of daily mass per area. Pigs need about 16% protein in their feed, but very young pigs require extra protein. They are typically grown to 120kg or so in 160 days, just after their daily growth peaks. Practically speaking, sows will bear two litters per year so it's best to calculate using 180 days and about 135kg live weight. The dressed weight is about 72% or 97 kg (alternatively, 28% slaughter waste or 38kg). About 37% of the live weight (50kg) is boneless meat and the rest (35% or 47kg) is skin, fat, organs and bone. If your cultural norms allow eating offal, cheek, feet, etc. and if you recover all extra fat as lard then you might net another 3-5% edible meat and about the same amount of lard. Pork bones are excellent for stock since they are heavy and thick, so this nonmeat category is not waste but it's also not considered for calorie content.

 The area for each pig seems to be about 0.8m² for good FCR. There are other areas needed for breeding and nursing plus associated storage of water, feed and waste so let;s call it 1m² per pig. Some producers call for 3-4m² per pig. We'll use 1m² mainly because most of the area devoted to the pig is in hydroponics; if the pen sizes need to be doubled it's not catastrophic. So, 50kg in 180 days on 1 m² is 278 g/m²*day. We will assume an FCR of 3.5 or 473kg of feed at an average of 18% protein. This will be made of mixed ag waste (assumed to be 10% protein) and insect meal (45% protein) with spirulina for vitamins/minerals. We will need 550kg ag waste (of which 34% is fed to insects), or an average of 3.056kg per day. A single person's expected ag waste is about 80% of that, so one person's diet could co-produce 222 grams of pork a day. On a per-kg waste basis that's 90 grams of meat.

Cows are raised both for meat and for milk. (Yes, technically a cow is a female animal 3+ years old that had at least 1 calf, but unfortunately there is no generic singular term for members of bos taurus. I will use "cow" as the common singular form of "cattle".) To handle this properly we need to consider a dairy herd (Holstein) with veal as the main meat output. Genetic diversity would not be difficult as long as there is trade with Earth; flash-frozen bull semen can be imported for insemination. Dairy cows lactate for 10-12 months followed by a 2-month dry cycle. Modern dairy farms take calves from their mothers within hours and feed them milk replacement products; in our case it is better to leave them together for two weeks to consume colostrum, acquire immunities and to improve health. The highest-yielding cattle produce 12,000 L or more per lactation, but the average is closer to 7,500. Let's assume we will do no better than 10,000 L (10,300 kg) over a 14-month cycle (about 20.4kg per day averaged across the herd). A herd with 100 producing cows will have 120 total cows plus 2-3 bulls and four second-year heifers preparing to be bred. One could get by with half that number, but less than a third of that makes one very reliant on backup genetic stock. Herds cull about 20% of their adults per year, so at minimum we should retain 24 females and 1 male through their first year. On a 14-month cycle, 85.7% of the herd will bear young in one year. About one fourth of culls are due to reproductive problems, so we can assume 95% of cows with the opportunity to give birth will do so. That should be 97-98 calves, with about a 1 in 200 chance of twins. They will bear equal numbers of each sex on average, so 48-49 males and the same count of females. The top 50% of females by appearance will be raised for milk, while the top 1 or 2 males will be raised as potential breeding bulls. That leaves 72 calves per year to raise for meat. All of these will need a milk replacement for 3-4 weeks and then will switch to normal feed. The producing cows need high protein at the start of their cycle (18%) tapering off to about 14%. Calves can handle 14% protein. The feed efficiency for milk is around 1.5 (an FCR of 0.67; this is a whole herd value including dry heifers) so our 125-member herd produces 883 tons of milk and consumes 592 tons of feed in a year. The FCR for meat cows is about 8 and not likely to go much lower without radical steps. The replacement heifers and bull need to reach about 390kg, requiring 78 tons of feed. The other calves can be slaughtered at 20-22 weeks / 220kg / 127 tons feed or they can be raised all the way to 500kg in about a year and a half for 288 tons of feed.

 So, the dairy side consumes 592 tons of feed a year to produce 883 tons of milk. That will require 665 tons of biomass, of which 172 tons is fed to insects for protein. Cows like to rest and will need 3.34m² for a freestall (this is the minimum possible area per adult animal); they also need about 0.6 meters of space along the trough. In total, expect about 13.5m² for each cow or 1,687.5m² for the herd and production of 1.434kg/m²*day. On a per-kg waste basis that's 1.328kg milk. The herd will also cull 24 adult animals weighing 680kg each, yielding 6,528kg meat or 10.6 g/m²*day. On a per-kg waste basis that's 9.8 grams of meat, though it is co-produced with the milk.

 The beef side requires a bit less space than the dairy side, perhaps 10m² per animal (particularly since the population is evenly distributed by age). The 72 animals could be harvested as veal at 20-22 weeks and 220kg or as beef at 18 months and 500kg. The main difference is space; for veal the herd needs 360m² while for beef 1,080m² are required. FCR and meat yield are similar, though veal might have a percentage point or two advantage. Veal would yield 6,336kg meat or 48.2 g/m²*day and consume 126.7 tons of feed (142.3 tons biomass). On a per-kg waste basis that's 44.5 grams of meat. Beef would yield 14,400kg meat or 36.5 g/m²*day and consume 288 tons of feed (323.5 tons biomass). On a per-kg waste basis that's also 44.5 grams of meat, just not as space-efficient.


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  2. posted at:

    I think once this series is done I'll make a round-up post with the results all in one place, without the walls of text.